Methods For The Detection, Analysis And Isolation of Nascent Proteins

ABSTRACT

This invention relates to non-radioactive markers that facilitate the detection and analysis of nascent proteins translated within cellular or cell-free translation systems. Nascent proteins containing these markers can be rapidly and efficiently detected, isolated and analyzed without the handling and disposal problems associated with radioactive reagents. Preferred markers are dipyrrometheneboron difluoride (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes.

FIELD OF THE INVENTION

This invention relates to non-radioactive markers that facilitate thedetection and analysis of nascent proteins translated within cellular orcell-free translation systems. Nascent proteins containing these markerscan be rapidly and efficiently detected, isolated and analyzed withoutthe handling and disposal problems associated with radioactive reagents.

BACKGROUND OF THE INVENTION

Cells contain organelles, macromolecules and a wide variety of smallmolecules. Except for water, the vast majority of the molecules andmacromolecules can be classified as lipids, carbohydrates, proteins ornucleic acids. Proteins are the most abundant cellular components andfacilitate many of the key cellular processes. They include enzymes,antibodies, hormones, transport molecules and components for is thecytoskeleton of the cell.

Proteins are composed of amino acids arranged into linear-polymers orpolypeptides. In living systems, proteins comprise over twenty commonamino acids. These twenty or so amino acids are generally termed thenative amino acids. At the center of every amino acid is the alphacarbon atom (Cα) which forms four bonds or attachments with othermolecules (FIG. 1). One bond is a covalent linkage to an amino group(NH₂) and another to a carboxyl group (COOH) which both participate inpolypeptide formation. A third bond is nearly always linked to ahydrogen atom and the fourth to a side chain which imparts variabilityto the amino acid structure. For example, alanine is formed when theside chain is a methyl group (—CH₃) and a valine is formed when the sidechain is an isopropyl group (—CH(CH₃)₂). It is also possible tochemically synthesize amino acids containing different side-chains,however, the cellular protein synthesis system, with rare exceptions,utilizes native amino acids. Other amino acids and structurally similarchemical compounds are termed non-native and are generally not found inmost organisms.

A central feature of all living systems is the ability to produceproteins from amino acids. Basically, protein is formed by the linkageof multiple amino acids via peptide bonds such as the pentapeptidedepicted in FIG. 1B. Key molecules involved in this process aremessenger RNA (mRNA) molecules, transfer RNA (tRNA) molecules andribosomes (rRNA-protein complexes). Protein translation normally occursin living cells and in some cases can also be performed outside the cellin systems referred to as cell-free translation systems. In eithersystem, the basic process of protein synthesis is identical. Theextra-cellular or cell-free translation system comprises an extractprepared from the intracellular contents of cells. These preparationscontain those molecules which support protein translation and dependingon the method of preparation, post-translational events such asglycosylation and cleavages as well. Typical cells from which cell-freeextracts or in vitro extracts are made are Escherichia coli cells, wheatgerm cells, rabbit reticulocytes, insect cells and frog oocytes.

Both in vivo and in vitro syntheses involve the reading of a sequence ofbases on a mRNA molecule. The mRNA contains instructions for translationin the form of triplet codons. The genetic code specifies which aminoacid is encoded by each triplet codon. For each codon which specifies anamino acid, there normally exists a cognate tRNA molecule whichfunctions to transfer the correct amino acid onto the nascentpolypeptide chain. The amino acid tyrosine (Tyr) is coded by thesequence of bases UAU and UAC, while cysteine (Cys) is coded by UGU andUGC. Variability associated with the third base of the codon is commonand is called wobble.

Translation begins with the binding of the ribosome to mRNA (FIG. 2). Anumber of protein factors associate with the ribosome during differentphases of translation including initiation factors, elongation factorsand termination factors. Formation of the initiation complex is thefirst step of translation. Initiation factors contribute to theinitiation complex along with the mRNA and initiator tRNA and met) whichrecognizes the base sequence UAG. Elongation proceeds with charged tRNAsbinding to ribosomes, translocation and release of the amino acid cargointo the peptide chain. Elongation factors assist with the binding oftRNAs and in elongation of the polypeptide chain with the help ofenzymes like peptidyl transferase. Termination factors recognize a stopsignal, such as the base sequence UGA, in the message terminatingpolypeptide synthesis and releasing the polypeptide chain and the mRNAfrom the ribosome.

The structure of tRNA is often shown as a cloverleaf representation(FIG. 3A). Structural elements of a typical tRNA include an acceptorstem, a D-loop, an anticodon loop, a variable loop and a TΨC loop.Aminoacylation or charging of tRNA results in linking the carboxylterminal of an amino acid to the 2′-(or 3′-) hydroxyl group of aterminal adenosine base via an ester linkage. This process can beaccomplished either using enzymatic or chemical methods. Normally aparticular tRNA is charged by only one specific native amino acid. Thisselective charging, termed here enzymatic aminoacylation, isaccomplished by aminoacyl tRNA synthetases. A tRNA which selectivelyincorporates a tyrosine residue into the nascent polypeptide chain byrecognizing the tyrosine UAC codon will be charged by tyrosine with atyrosine-aminoacyl tRNA synthetase, while a tRNA designed to read theUGU codon will be charged by a cysteine-aminoacyl tRNA synthetase. Thesesynthetases have evolved to be extremely accurate in charging a tRNAwith the correct amino acid to maintain the fidelity of the translationprocess. Except in special cases where the non-native amino acid is verysimilar structurally to the native amino acid, it is necessary to usemeans other than enzymatic aminoacylation to charge a tRNA.

Molecular biologists routinely study the expression of proteins that arecoded for by genes. A key step in research is to express the products ofthese genes either in intact cells or in cell-free extracts.Conventionally, molecular biologists use radioactively labeled aminoacid residues such as ³⁵S-methionine as a means of detecting newlysynthesized proteins or so-called nascent proteins. These nascentproteins can normally be distinguished from the many other proteinspresent in a cell or a cell-free extract by first separating theproteins by the standard technique of gel electrophoresis anddetermining if the proteins contained in the gel possess the specificradioactively labeled amino acids. This method is simple and relies ongel electrophoresis, a widely available and practiced method. It doesnot require prior knowledge of the expressed protein and in general doesnot require the protein to have any special properties. In addition, theprotein can exist in a denatured or unfolded form for detection by gelelectrophoresis. Furthermore, more specialized techniques such asblotting to membranes and coupled enzymatic assays are not needed.Radioactive assays also have the advantage that the structure of thenascent protein is not altered or can be restored, and thus, proteinscan be isolated in a functional form for subsequent biochemical andbiophysical studies.

Radioactive methods suffer from many drawbacks related to theutilization of radioactively labeled amino acids. Handling radioactivecompounds in the laboratory always involves a health risk and requiresspecial laboratory safety procedures, facilities and detailed recordkeeping as well as special training of laboratory personnel. Disposal ofradioactive waste is also of increasing concern both because of thepotential risk to the public and the lack of radioactive waste disposalsites. In addition, the use of radioactive labeling is time consuming,in some cases requiring as much as several days for detection of theradioactive label. The long time needed for such experiments is a keyconsideration and can seriously impede research productivity. Whilefaster methods of radioactive detection are available, they areexpensive and often require complex image enhancement devices.

The use of radioactive labeled amino acids also does not allow for asimple and rapid means to monitor the production of nascent proteinsinside a cell-free extract without prior separation of nascent frompreexisting proteins. However, a separation step does not allow for theoptimization of cell-free activity. Variables including theconcentration of ions and metabolites and the temperature and the timeof protein synthesis cannot be adjusted.

Radioactive labeling methods also do not provide a means of isolatingnascent proteins in a form which can be further utilized. The presenceof radioactivity compromises this utility for further biochemical orbiophysical procedures in the laboratory and in animals. This is clearin the case of in vitro expression when proteins cannot be readilyproduced in vivo because the protein has properties which are toxic tothe cell. A simple and convenient method for the detection and isolationof nascent proteins in a functional form could be important in thebiomedical field if such proteins possessed diagnostic or therapeuticproperties. Recent research has met with some success, but these methodshave had numerous drawbacks.

Radioactive labeling methods also do not provide a simple and rapidmeans of detecting changes in the sequence of a nascent protein whichcan indicate the presence of potential disease causing mutations in theDNA which code for these proteins or fragments of these proteins.Current methods of analysis at the protein level rely on the use of gelelectrophoresis and radioactive detection which are slow and notamenable to high throughput analysis and automation. Such mutations canalso be detected by performing DNA sequence analysis on the gene codingfor a particular protein or protein fragment. However, this requireslarge regions of DNA to be sequenced, which is time-consuming andexpensive. The development of a general method which allows mutations tobe detected at the nascent protein level is potentially very importantfor the biomedical field.

Radioactive labeling methods also do not provide a simple and rapidmeans of studying the interaction of nascent proteins with othermolecules including compounds which might be have importance aspotential drugs. If such an approach were available, it could beextremely useful for screening large numbers of compounds against thenascent proteins coded for by specific genes, even in cases where thegenes or protein has not yet been characterized. In current technology,which is based on affinity electrophoresis for screening of potentialdrug candidates, both in natural samples and synthetic libraries,proteins must first be labeled uniformly with a specific marker whichoften requires specialized techniques including isolation of the proteinand the design of special ligand markers or protein engineering.

Special tRNAs, such as tRNAs which have suppressor properties,suppressor tRNAs, have been used in the process of site-directednon-native amino acid replacement (SNAAR) (C. Noren et al., Science244:182-188, 1989). In SNAAR, a unique codon is required on the mRNA andthe suppressor tRNA, acting to target a non-native amino acid to aunique site during the protein synthesis (PCT WO90/05785). However, thesuppressor tRNA must not be recognizable by the aminoacyl tRNAsynthetases present in the protein translation system (Bain et al.,Biochemistry 30:5411-21, 1991). Furthermore, site-specific incorporationof non-native amino acids is not suitable in general for detection ofnascent proteins in a cellular or cell-free protein synthesis system dueto the necessity of incorporating non-sense codons into the codingregions of the template DNA or the mRNA.

Products of protein synthesis may also be detected by using antibodybased assays. This method is of limited use because it requires that theprotein be folded into a native form and also for antibodies to havebeen previously produced against the nascent protein or a known proteinwhich is fused to the unknown nascent protein. Such procedures are timeconsuming and again require identification and characterization of theprotein. In addition, the production of antibodies and amino acidsequencing both require a high level of protein purity.

In certain cases, a non-native amino acid can be formed after the tRNAmolecule is aminoacylated using chemical reactions which specificallymodify the native amino acid and do not significantly alter thefunctional activity of the aminoacylated tRNA (Promega TechnicalBulletin No. 182; tRNA^(nscend)™: Non-radioactive Translation DetectionSystem, September 1993). These reactions are referred to aspost-aminoacylation modifications. For example, the c-amino group of thelysine linked to its cognate tRNA (tRNA^(LYS)), could be modified withan amine specific photoaffinity label (U. C. Krieg et al., Proc. Natl.Acad. Sci. USA 83:8604-08, 1986). These types of post-aminoacylationmodifications, although useful, do not provide a general means ofincorporating non-native amino acids into the nascent proteins. Thedisadvantage is that only those non-native amino acids that arederivatives of normal amino acids can be incorporated and only a fewamino acid residues have side chains amenable to chemical modification.More often, post-aminoacylation modifications can result in the tRNAbeing altered and produce a non-specific modification of the α-aminogroup of the amino acid (e.g. in addition to the ε-amino group) linkedto the tRNA. This factor can lower the efficiency of incorporation ofthe non-native amino acid linked to the tRNA. Non-specific,post-aminoacylation modifications of tRNA structure could alsocompromise its participation in protein synthesis. Incomplete chainformation could also occur when the α-amino group of the amino acid ismodified.

In certain other cases, a nascent protein can be detected because of itsspecial and unique properties such as specific enzymatic activity,absorption or fluorescence. This approach is of limited use since mostproteins do not have special properties with which they can be easilydetected. In many cases, however, the expressed protein may not havebeen previously characterized or even identified, and thus, itscharacteristic properties are unknown.

SUMMARY OF THE INVENTION

The present invention overcomes the problems and disadvantagesassociated with current strategies and designs and provides methods forthe labeling, detection, quantitation, analysis and isolation of nascentproteins produced in a cell-free or cellular translation system withoutthe use of radioactive amino acids or other radioactive labels. Oneembodiment of the invention is directed to methods for detecting nascentproteins translated in a translation system. A tRNA molecule isaminoacylated with a fluorescent marker to create a misaminoacylatedtRNA. The misaminoacylated, or charged, tRNA can be formed by chemical,enzymatic or partly chemical and partly-enzymatic techniques which placea fluorescent marker into a position on the tRNA molecule from which itcan be transferred into a growing peptide chain. Markers may comprisenative or non-native amino acids with fluorescent moeities, amino acidanalogs or derivatives with fluorescent moeities, detectable labels,coupling agents or combinations of these components with fluoresecentmoieties. The misaminoacylated tRNA is introduced to the translationsystem such as a cell-free extract, the system is incubated and thefluorescent marker incorporated into nascent proteins.

It is not intended that the present invention be limited to the natureof the particular fluorescent moeity. A variety of fluorescent compoundsare contemplated, including fluorescent compounds that have beenderivatized (e.g. with NHS) to be soluble (e.g. NHS-derivatives ofcoumarin). Nonetheless, compared to many other fluorophores with highquantum yields, several BODIPY compounds and reagents have beenempirically found to have the additional important and unusual propertythat they can be incorporated with high efficiency into nascent proteinsfor both UV and visible excited fluorescence detection. These methodsutilitzing fluorescent moeities may be used to detect, isolate andquantitate such nascent proteins as recombinant gene products, genefusion products, truncated proteins caused by mutations in human genes,enzymes, cytokines, hormones, immunogenic proteins, human proteins,carbohydrate and lipid binding proteins, nucleic acid binding proteins,viral proteins, bacterial proteins, parasitic proteins and fragments andcombinations thereof.

Another embodiment of the invention is directed to methods for labelingnascent proteins at their amino terminus. An initiator tRNA molecule,such as methionine initiator tRNA or formylmethionine-initiator tRNA ismisaminoacylated with a fluorescent moeity (e.g. a BODIPY moiety) andintroduced to a translation system. The system is incubated and markeris incorporate at the amino terminus of the nascent proteins. Nascentproteins containing marker can be detected, isolated and quantitated.Markers or parts of markers may be cleaved from the nascent proteinswhich substantially retain their native configuration and arefunctionally active.

Thus, the present invention contemplates compositions, methods andsystems. In terms of compositions, the present invention specificallycontemplates a tRNA molecule misaminoacylated with a BODIPY marker.

In one embodiment, the present invention contemplates a method,comprising: a) providing a tRNA molecule and a BODIPY marker; and b)aminoacylating said tRNA molecule with said BODIPY marker to create amisaminoacylated tRNA. In a particular embodiment, the method furthercomprises c) introducing said misaminoacylated tRNA into a translationsystem under conditions such that said marker is incorporated into anascent protein. In yet another embodiment, the method further comprisesd) detecting said nascent protein containing said marker. In stillanother embodiment, the method further comprises e) isolating saiddetected nascent protein.

The present invention contemplates aminoacylation of the tRNA moleculeby chemical or enzymatic misaminoacylation. The present invention alsocontemplates embodiments wherein two or more different misaminoacylatedtRNAs are introduced into the translation system. In a preferredembodiment, the nascent protein detected (by virtue of the incorporatedmarker) is functionally active.

It is not intended that the present invention be limited by theparticular nature of the nascent protein. In one embodiment, the presentinvention contemplates a method for detecting nascent proteins which areconjugated to the mRNA message which codes for all or part of thenascent protein. In general, a variety of modifications of the nascentprotein are envisioned including post-translational modifications,proteolysis, attachment of an oligonucleotide through a puromycin linkerto the C-terminus of the protein, and interaction of the nascent proteinwith other components of the translation system including those whichare added exogenously.

It is not intended that the present invention be limited by theparticular nature of the tRNA molecule. In one embodiment, the tRNAmolecule is an initiator tRNA molecule. In another embodiment, the tRNAmolecule is a suppressor tRNA molecule.

The present invention also contemplates kits. In one embodiment, the kitcomprises a) a first containing means (e.g. tubes, vials, etc)containing at least one component of a protein synthesis system; and b)a second containing means containing a misaminoacylated tRNA, whereinsaid tRNA is misaminoacylated with a BODIPY marker. Such kits mayinclude initiator tRNA and/or suppressor tRNA. Importantly, the kit isnot limited to the particular components of said protein synthesissystem; a variety of components are contemplated (e.g. ribosomes).

Another embodiment of the invention is directed to methods for detectingnascent proteins translated in a translation system. A tRNA molecule isaminoacylated with one component of a binary marker system. Themisaminoacylated, or charged, tRNA can be formed by chemical, enzymaticor partly chemical and partly enzymatic techniques which place acomponent of a binary marker system into a position on the tRNA moleculefrom which it can be transferred into a growing peptide chain. Thecomponent of the binary marker system may comprise native or non-nativeamino acids, amino acid analogs or derivatives, detectable labels,coupling agents or combinations of these components. Themisaminoacylated tRNA is introduced to the translation system such as acell-free extract, the system is incubated and the marker incorporatedinto nascent proteins. The second component of the binary marker systemis then introduced making the first component incorporated into thenascent protein specifically detectable. These methods may be used todetect, isolate and quantitate such nascent proteins as recombinant geneproducts, gene fusion products, enzymes, cytokines, hormones,immunogenic proteins, human proteins, carbohydrate and lipid bindingproteins, nucleic acid binding proteins, viral proteins, bacterialproteins, parasitic proteins and fragments and combinations thereof.

It is not intended that the present invention be limited to a particulartranslation system. In one embodiment, a cell-free translation system isselected from the group consisting of Escherichia coli lysates, wheatgerm extracts, insect cell lysates, rabbit reticulocyte lysates, frogoocyte lysates, dog pancreatic lysates, human cell lysates, mixtures ofpurified or semi-purified translation factors and combinations thereof.It is also not intended that the present invention be limited to theparticular reaction conditions employed. However, typically thecell-free translation system is incubated at a temperature of betweenabout 25° C. to about 45° C. The present invention contemplates bothcontinuous flow systems or dialysis systems.

Another embodiment of the invention is directed to methods for thedetection of nascent proteins translated in a cellular or cell-freetranslation system using non-radioactive markers which have detectableelectromagnetic spectral properties. As before, a non-radioactive markeris misaminoacylated to a tRNA molecule and the misaminoacylated tRNA isadded to the translation system. The system is incubated to incorporatemarker into the nascent proteins. Nascent proteins containing marker canbe detected from the specific electromagnetic spectral property of themarker. Nascent proteins can also be isolated by taking advantage ofunique properties of these markers or by conventional means such aselectrophoresis, gel filtration, high-pressure or fast-pressure liquidchromatography, affinity chromatography, ion exchange chromatography,chemical extraction, magnetic bead separation, precipitation orcombinations of these techniques.

Another embodiment of the invention is directed to the synthesis ofnascent proteins containing markers which have reporter properties whenthe reporter is brought into contact with a second agent. Reportermarkers are chemical moieties which have detectable electromagneticspectral properties when incorporated into peptides and whose spectralproperties can be distinguished from unincorporated markers and markersattached to tRNA molecules. As before, tRNA molecules aremisaminoacylated, this time using reported markers. The misaminoacylatedtRNAs are added to a translation system and incubated to incorporatemarker into the peptide. Reporter markers can be used to follow theprocess of protein translation and to detect and quantitate nascentproteins without prior isolation from other components of the proteinsynthesizing system.

Another embodiment of the invention is directed to compositionscomprised of nascent proteins translated in the presence of markers,isolated and, if necessary, purified in a cellular or cell-freetranslation system. Compositions may further comprise a pharmaceuticallyacceptable carrier and be utilized as an immunologically activecomposition such as a vaccine, or as a pharmaceutically activecomposition such as a drug, for use in humans and other mammals.

Another embodiment of the invention is directed to methods for detectingnascent proteins translated in a translation system by using massspectrometry. A non-radioactive marker of known mass is misaminoacylatedto a tRNA molecule and the misaminoacylated tRNA is added to thetranslation system. The system is incubated to incorporate the massmarker into the nascent proteins. The mass spectrum of the translationsystem is then measured. The presence of the nascent protein can bedirectly detected by identifying peaks in the mass spectrum of theprotein synthesis system which correspond to the mass of the unmodifiedprotein and a second band at a higher mass which corresponds to the massof the nascent protein plus the modified amino acid containing the massof the marker. When the mass marker is photocleavable, the assignment ofthe second band to a nascent protein containing the mass marker can beverified by removing the marker with light.

Another embodiment of the invention is directed to methods for detectingnascent proteins with mutations which are translated in a translationsystem. RNA or DNA coding for the protein which may contain a possiblemutation is added to the translation system. The system is incubated tosynthesize the nascent proteins. The nascent protein is then separatedfrom the translation system using an affinity marker located at or closeto the N-terminal end of the protein. The protein is then analyzed forthe presence of a detectable marker located at or close to theN-terminal of the protein (N-terminal marker). A separate measurement isthen made on a sequence dependent detectable marker located at or closeto the C-terminal end of the protein (C-terminal marker). A comparisonis then made of the level of incorporation of the N-terminal andC-terminal markers in the nascent protein. It is not intended that thepresent invention be limited by the nature of the N- and C-terminalmarkers, or the type of affinity marker utilized. A variety of markersare contemplated. In one embodiment, the affinity marker comprises anepitope recognized by an antibody or other binding molecule. In oneembodiment, the N-terminal marker comprises a fluorescent marker (e.g. aBODIPY marker), while the C-terminal marker comprises a metal bindingregion (e.g. His tag).

The present invention contemplates a variety of methods wherein thethree markers (e.g. the N- and C-terminal markers and the affinitymarkers) are introduced into a nascent protein. In one embodiment, themethod comprises: a) providing i) a misaminoacylated initiator tRNAmolecule which only recognizes the first AUG codon that serves toinitiate protein synthesis, said misaminoacylated initiator tRNAmolecule comprising a first marker, and ii) a nucleic acid templateencoding a protein, said protein comprising a C-terminal marker and (insome embodiments) an affinity marker; b) introducing saidmisaminoacylated initiator tRNA to a translation system comprising saidtemplate under conditions such that a nascent protein is generated, saidprotein comprising said first marker, said C-terminal marker and (insome embodiments) said affinity marker. In one embodiment, the methodfurther comprises, after step b), isolating said nascent protein.

In another embodiment, the method comprises: a) providing i) amisaminoacylated initiator tRNA molecule which only recognizes the firstAUG codon that serves to initiate protein synthesis, saidmisaminoacylated initiator tRNA molecule comprising a first marker, andii) a nucleic acid template encoding a protein, said protein comprisinga C-terminal marker and (in some embodiments) an affinity marker; b)introducing said misaminoacylated initiator tRNA to a translation systemcomprising said template under conditions such that a nascent protein isgenerated, said protein comprising said first marker at the N-terminusof said protein, a C-terminal marker, and (in some embodiments) saidaffinity marker adjacent to said first marker. In one embodiment, themethod further comprises, after step b), isolating said nascent protein.

In yet another embodiment, the method comprises: a) providing i) amisaminoacylated tRNA molecule which only recognizes the first codondesigned to serve to initiate protein synthesis, said misaminoacylatedinitiator tRNA molecule comprising a first marker, and ii) a nucleicacid template encoding a protein, said protein comprising a C-terminalmarker and (in some embodiments) an affinity marker; b) introducing saidmisaminoacylated initiator tRNA to a translation system comprising saidtemplate under conditions such that a nascent protein is generated, saidprotein comprising said first marker, said C-terminal marker and (insome embodiments) said affinity marker. In one embodiment, the methodfurther comprises, after step b), isolating said nascent protein.

In still another embodiment, the method comprises: a) providing i) amisaminoacylated tRNA molecule which only recognizes the first codondesigned to serve to initiate protein synthesis, said misaminoacylatedinitiator tRNA molecule comprising a first marker, and ii) a nucleicacid template encoding a protein, said protein comprising a C-terminalmarker and (in some embodiments) an affinity marker; b) introducing saidmisaminoacylated initiator tRNA to a translation system comprising saidtemplate under conditions such that a nascent protein is generated, saidprotein comprising said first marker at the N-terminus of said protein,a C-terminal marker, and (in some embodiments) said affinity markeradjacent to said first marker. In one embodiment, the method furthercomprises, after step b), isolating said nascent protein.

The present invention also contemplates embodiments where only twomarkers are employed (e.g. a marker at the N-terminus and a marker atthe C-terminus). In one embodiment, the nascent protein isnon-specifically bound to a solid support (e.g. beads, microwells,strips, etc.), rather than by the specific interaction of an affinitymarker. In this context, “non-specific” binding is meant to indicatethat binding is not driven by the uniqueness of the sequence of thenascent protein. Instead, binding can be by charge interactions. In oneembodiment, the present invention contemplates that the solid support ismodified (e.g. functionalized to change the charge of the surface) inorder to capture the nascent protein on the surface of the solidsupport. In one embodiment, the solid support is poly-L-lysine coated.In yet another embodiment, the solid support is nitrocellulose (e.g.strips, nicrocellulose containing microwells, etc.). Regardless of theparticular nature of the solid support, the present inventioncontemplates that the nascent protein containing the two markers iscaptured under conditions that permit the ready detection of themarkers.

In both the two marker and three marker embodiments described above, thepresent invention contemplates that one or more of the markers will beintroduced into the nucleic acid template by primer extension or PCR. Inone embodiment, the present invention contemplates a primer comprising(on or near the 5′-end) a promoter, a ribosome binding site (“RBS”), anda start codon (e.g. ATG), along with a region of complementarity to thetemplate. In another embodiment, the present invention contemplates aprimer comprising (on or near the 5′-end) a promoter, a ribosome bindingsite (“RBS”), a start codon (e.g. ATG), a region encoding an affinitymarker, and a region of complementarity to the template. It is notintended that the present invention be limited by the length of theregion of complementarity; preferably, the region is greater than 8bases in length, more preferably greater than 15 bases in length, andstill more preferably greater than 20 bases in length.

It is also not intended that the present invention be limited by theribosome binding site. In one embodiment, the present inventioncontemplates primers comprising the Kozak sequence, a string ofnon-random nucleotides (consensus sequence 5′-GCCA/GCCATGG-3′) which arepresent before the translation initiating first ATG in majority of themRNAs which are transcribed and translated in an eukarytic cells. See M.Kozak, Cell 44:283-292 (1986). In another embodiment, the presentinvention contemplates a primer comprising the the prokaryotic mRNAribosome binding site, which usually contains part or all of apolypurine domain UAAGGAGGU known as the Shine-Dalgarno (SD) sequencefound just 5′ to the translation initiation codon: mRNA5′-UAAGGAGGU-N₅₋₁₀-AUG.

For PCR, two primers are used. In one embodiment, the present inventioncontemplates as the forward primer a primer comprising (on or near the5′-end) a promoter, a ribosome binding site (“RBS”), and a start codon(e.g. ATG), along with a region of complementarity to the template. Inanother embodiment, the present invention contemplates as the forwardprimer a primer comprising (on or near the 5′-end) a promoter, aribosome binding site (“RBS”), a start codon (e.g. ATG), a regionencoding an affinity marker, and a region of complementarity to thetemplate. The present invention contemplates that the reverse primer, inone embodiment, comprises (at or near the 5′-end) one or more stopcondons and a region encoding a C-terminus marker (such as a HIS-tag).

Another embodiment of the invention is directed to methods for detectingby electrophoresis (e.g. capillary electrophoresis) the interaction ofmolecules with nascent proteins which are translated in a translationsystem. A tRNA misaminoacylated with a detectable marker is added to theprotein synthesis system. The system is incubated to incorporate thedetectable marker into the nascent proteins. One or more specificmolecules are then combined with the nascent proteins (either before orafter isolation) to form a mixture containing nascent proteins/moleculeconjugates. Aliquots of the mixture are then subjected to capillarlyelectrophoresis. Nascent proteins/molecule conjugates are identified bydetecting changes in the electrophoretic mobility of nascent proteinswith incorporated markers.

Other embodiments and advantages of the invention are set forth, inpart, in the description which follows and, in part, will be obviousfrom this description, or may be learned from the practice of theinvention.

Definitions

To facilitate understanding of the invention, a number of terms aredefined below.

The term “gene” refers to a DNA sequence that comprises control andcoding sequences necessary for the production of a polypeptide orprecursor. The polypeptide can be encoded by a full length codingsequence or by any portion of the coding sequence so long as the desiredenzymatic activity is retained.

The term “wild-type” refers to a gene or gene product which has thecharacteristics of that gene or gene product when isolated from anaturally occurring source. A wild-type gene is that which is mostfrequently observed in a population and is thus arbitrarily designed the“normal” or “wild-type” form of the gene. In contrast, the term“modified” or “mutant” refers to a gene or gene product which displaysmodifications in sequence and or functional properties (i.e., alteredcharacteristics) when compared to the wild-type gene or gene product. Itis noted that naturally-occurring mutants can be isolated; these areidentified by the fact that they have altered characteristics whencompared to the wild-type gene or gene product.

The term “oligonucleotide” as used herein is defined as a moleculecomprised of two or more deoxyribonucleotides or ribonucleotides,preferably more than three, and usually more than ten. The exact sizewill depend on many factors, which in turn depends on the ultimatefunction or use of the oligonucleotide. The oligonucleotide may begenerated in any manner, including chemical synthesis, DNA replication,reverse transcription, or a combination thereof.

Because mononucleotides are reacted to make oligonucleotides in a mannerSuch that the 5’ phosphate of one mononucleotide pentose ring isattached to the 3′ oxygen of its neighbor in one direction via aphosphodiester linkage, an end of an oligonucleotide is referred to asthe “5′ end” if its 5′ phosphate is not linked to the 3′ oxygen of amononucleotide pentose ring and as the “3′ end” if its 3′ oxygen is notlinked to a 5′ phosphate of a subsequent mononucleotide pentose ring. Asused herein, a nucleic acid sequence, even if internal to a largeroligonucleotide, also may have 5′ and 3′ ends.

The term “primer” refers to an oligonucleotide which is capable ofacting as a point of initiation of synthesis when placed underconditions in which primer extension is initiated. An oligonucleotide“primer” may occur naturally, as in a purified restriction digest or maybe produced synthetically.

A primer is selected to have on its 3′ end a region that is“substantially” complementary to a strand of specific sequence of thetemplate. A primer must be sufficiently complementary to hybridize witha template strand for primer elongation to occur. A primer sequence neednot reflect the exact sequence of the template. For example, anon-complementary nucleotide fragment may be attached to the 5′ end ofthe primer, with the remainder of the primer sequence beingsubstantially complementary to the strand. Non-complementary bases orlonger sequences can be interspersed into the primer, provided that theprimer sequence has sufficient complementarity with the sequence of thetemplate to hybridize and thereby form a template primer complex forsynthesis of the extension product of the primer.

As used herein, the terms “hybridize” and “hybridization” refers to theannealing of a complementary sequence to the target nucleic acid. Theability of two polymers of nucleic acid containing complementarysequences to find each other and anneal through base pairing interactionis a well-recognized phenomenon. Marmur and Lane, Proc. Natl. Acad. Sci.USA 46:453 (1960) and Doty et al., Proc. Natl. Acad. Sci. USA 46:461(1960). The terms “annealed” and “hybridized” are used interchangeablythroughout, and are intended to encompass any specific and reproducibleinteraction between an oligonucleotide and a target nucleic acid,including binding of regions having only partial complementarity.

The complement of a nucleic acid sequence as used herein refers to anoligonucleotide which, when aligned with the nucleic acid sequence suchthat the 5′ end of one sequence is paired with the 3′ end of the other,is in “antiparallel association.” Certain bases not commonly found innatural nucleic acids may be included in the nucleic acids of thepresent invention and include, for example, inosine and 7-deazaguanine.Complementarity need not be perfect; stable duplexes may containmismatched base pairs or unmatched bases. Those skilled in the art ofnucleic acid technology can determine duplex stability empiricallyconsidering a number of variables including, for example, the length ofthe oligonucleotide, base composition and sequence of theoligonucleotide, ionic strength and incidence of mismatched base pairs.

The stability of a nucleic acid duplex is measured by the meltingtemperature, or “T_(m).” The T_(m) of a particular nucleic acid duplexunder specified conditions is the temperature at which on average halfof the base pairs have disassociated.

The term “probe” as used herein refers to an oligonucleotide which formsa duplex structure or other complex with a sequence in another nucleicacid, due to complementarity or other means of reproducible attractiveinteraction, of at least one sequence in the probe with a sequence inthe other nucleic acid.

“Oligonucleotide primers matching or complementary to a gene sequence”refers to oligonucleotide primers capable of facilitating thetemplate-dependent synthesis of single or double-stranded nucleic acids.Oligonucleotide primers matching or complementary to a gene sequence maybe used in PCRs, RT-PCRs and the like. As noted above, anoligonucleotide primer need not be perfectly complementary to a targetor template sequence. A primer need only have a sufficient interactionwith the template that it can be extended by template-dependentsynthesis.

As used herein, the term “poly-histidine tract” or (HIS-tag) refers tothe presence of two to ten histidine residues at either the amino- orcarboxy-terminus of a nascent protein A poly-histidine tract of six toten residues is preferred. The poly-histidine tract is also definedfunctionally as being a number of consecutive histidine residues addedto the protein of interest which allows the affinity purification of theresulting protein on a nickel-chelate column, or the indentification ofa protein terminus through the interaction with another molecule (e.g.an antibody reactive with the HIS-tag).

DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows the structure of (A) an amino acid and (B) a peptide.

FIG. 2 provides a description of the molecular steps that occur duringprotein synthesis in a cellular or cell-free system.

FIG. 3 shows a structure of (A) a tRNA molecule and (B) approachesinvolved in the aminoacylation of tRNAs.

FIG. 4 is a schematic representation of the method of detecting nascentproteins using fluorescent marker amino acids.

FIG. 5 shows schemes for synthesis and misaminoacylation to tRNA of twodifferent marker amino acids, dansyllysine (scheme 1) and coumarin(scheme 2), with fluorescent properties suitable for the detection ofnascent proteins using gel electrophoresis and UV illumination.

FIG. 6(A) shows chemical compounds containing the 2-nitrobenzyl moiety,and FIG. 6(B) shows cleavage of substrate from a nitrobenzyl linkage.

FIG. 7 provides examples of photocleavable markers.

FIG. 8(A) shows chemical variations of PCB, and FIG. 8(B) depictspossible amino acid linkages.

FIG. 9 shows the photolysis of PCB.

FIG. 10 is a schematic representation of the method for monitoring theproduction of nascent proteins in a cell-free protein expression systemswithout separating the proteins.

FIG. 11(A) provides examples of non-native amino acids with reporterproperties, FIG. 11(B) shows participation of a reporter in proteinsynthesis, and FIG. 11(C) shows synthesis of a reporter.

FIG. 12 shows structural components of photocleavable biotin.

FIG. 13 is a schematic representation of the method for introduction ofmarkers at the N-termini of nascent proteins.

FIG. 14 provides a description of the method of detection and isolationof marker in nascent proteins.

FIG. 15 shows the steps in one embodiment for the synthesis ofPCB-lysine.

FIG. 16 provides an experimental strategy for the misaminoacylation oftRNA.

FIG. 17 illustrates dinucleotide synthesis including (i) deoxycytidineprotection, (ii) adenosine protection, and (iii) dinucleotide synthesis.

FIG. 18 depicts aminoacylation of a dinucleotide using marker aminoacids.

FIG. 19 shows the structure of dipyrrometheneboron difluoride(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes.

FIG. 20 is a photograph of a gel showing the incorporation of variousfluorsecent molecules into hemolysin during translation.

FIG. 21A-B shows the incorporation if BODIPY-FL into various proteins.FIG. 21A shows the results visualized using laser based MolecularDynamics FluorImager 595, while FIG. 21B shows the results visualizedusing a UV-transilluminator.

FIG. 22A shows a time course of fluorescence labeling. FIG. 22B showsthe SDS-PAGE results of various aliquotes of the translation mixture,demonstrating the sensitivity of the system.

FIG. 23A is a bar graph showing gel-free quantitation of an N-terminalmarker introduced into a nascent protein in accordance with the methodof the present invention. FIG. 23B is a bar graph showing gel-freequantitation of an C-terminal marker of a nascent protein quantitated inaccordance with the method of the present invention.

FIG. 24 shows gel results for protease treated and untreated protein.

FIG. 25 shows gel results for protein treated with RBCs and untreatedprotein.

FIG. 26A is a gel showing the incorporation of various fluorescentmolecules into α-hemolysin in E. coli translation system usingmisaminoacylated lysyl-tRNA^(lys).

FIG. 26B shows the incorporation of various fluorescent molecules intoluciferase in a TnT wheat germ system using misaminoacylatedlysyl-tRNA^(lys).

FIG. 27 shows gel results of in vitro translation of α-HL carried out inthe presence of various fluorescent-tRNAs, including atRNA-coumarinderivative.

FIGS. 28A and 28B show mobility shift results by capillaryelectrophoresis.

FIG. 29 are gel results of in vitro translation results wherein threemarkers were introduced into a nascent protein.

DESCRIPTION OF THE INVENTION

As embodied and described herein, the present invention comprisesmethods for the non-radioactive labeling and detection of the productsof new or nascent protein synthesis, and methods for the isolation ofthese nascent proteins from preexisting proteins in a cellular orcell-free translation system. As radioactive labels are not used, thereare no special measures which must be taken to dispose of wastematerials. There is also no radioactivity danger or risk which wouldprevent further utilization of the translation product as occurs whenusing radioactive labels and the resulting protein product may be useddirectly or further purified. In addition, no prior knowledge of theprotein sequence or structure is required which would involve, forexample, unique suppressor tRNAs. Further, the sequence of the gene ormRNA need not be determined. Consequently, the existence of non-sensecodons or any specific codons in the coding region of the mRNA is notnecessary. Any tRNA can be used, including specific tRNAs for directedlabeling, but such specificity is not required. Unlikepost-translational labeling, nascent proteins are labeled withspecificity and without being subjected to post-translationalmodifications which may effect protein structure or function.

One embodiment of the invention is directed to a method for labelingnascent proteins synthesized in a translation system. These proteins arelabeled while being synthesized with detectable markers which areincorporated into the peptide chain. Markers which are aminoacylated totRNA molecules, may comprise native amino acids, non-native amino acids,amino acid analogs or derivatives, or chemical moieties. These markersare introduced into nascent proteins from the resulting misaminoacylatedtRNAs during the translation process. Aminoacylation is the processwhereby a tRNA molecule becomes charged. When this process occurs invivo, it is referred to as natural aminoacylation and the resultingproduct is an aminoacylated tRNA charged with a native amino acid. Whenthis process occurs through artificial means, it is calledmisaminoacylation and a tRNA charged with anything but a native aminoacid molecule is referred to as a misaminoacylated tRNA.

According to the present method, misaminoacylated tRNAs are introducedinto a cellular or cell-free protein synthesizing system, thetranslation system, where they function in protein synthesis toincorporate detectable marker in place of a native amino acid in thegrowing peptide chain. The translation system comprises macromoleculesincluding RNA and enzymes, translation, initiation and elongationfactors, and chemical reagents. RNA of the system is required in threemolecular forms, ribosomal RNA (rRNA), messenger RNA (mRNA) and transferRNA (tRNA). mRNA carries the genetic instructions for building a peptideencoded within its codon sequence. tRNAs contain specific anti-codonswhich decode the mRNA and individually carry amino acids into positionalong the growing peptide chain. Ribosomes, complexes of rRNA andprotein, provide a dynamic structural framework on which the translationprocess, including translocation, can proceed. Within the cell,individualized aminoacyl tRNA synthetases bind specific amino acids totRNA molecules carrying the matching anti-codon creating aminoacylatedor charged tRNAs by the process of aminoacylation. The process oftranslation including the aminoacylation or charging of a tRNA moleculeis described in Molecular Cell Biology (J. Darnell et al. editors,Scientific American Books, N.Y., N.Y. 1991), which is herebyspecifically incorporated by reference. Aminoacylation may be natural orby artificial means utilizing native amino acids, non-native amino acid,amino acid analogs or derivatives, or other molecules such as detectablechemicals or coupling agents. The resulting misaminoacylated tRNAcomprises a native amino acid coupled with a chemical moiety, non-nativeamino acid, amino acid derivative or analog, or other detectablechemicals. These misaminoacylated tRNAs incorporate their markers intothe growing peptide chain during translation forming labeled nascentproteins which can be detected and isolated by the presence or absenceof the marker.

Any proteins that can be expressed by translation in a cellular orcell-free translation system may be nascent proteins and consequently,labeled, detected and isolated by the methods of the invention. Examplesof such proteins include enzymes such as proteolytic proteins,cytokines, hormones, immunogenic proteins, carbohydrate or lipid bindingproteins, nucleic acid binding proteins, human proteins, viral proteins,bacterial proteins, parasitic proteins and fragments and combinations.These methods are well adapted for the detection of products ofrecombinant genes and gene fusion products because recombinant vectorscarrying such genes generally carry strong promoters which transcribemRNAs at fairly high levels. These mRNAs are easily translated in atranslation system.

Translation systems may be cellular or cell-free, and may be prokaryoticor eukaryotic. Cellular translation systems include whole cellpreparations such as permeabilized cells or cell cultures wherein adesired nucleic acid sequence can be transcribed to mRNA and the mRNAtranslated.

Cell-free translation systems are commercially available and manydifferent types and systems are well-known. Examples of cell-freesystems include prokaryotic lysates such as Escherichia coli lysates,and eukaryotic lysates such as wheat germ extracts, insect cell lysates,rabbit reticulocyte lysates, frog oocyte lysates and human cell lysates.Eukaryotic extracts or lysates may be preferred when the resultingprotein is glycosylated, phosphorylated or otherwise modified becausemany such modifications are only possible in eukaryotic systems. Some ofthese extracts and lysates are available commercially (Promega; Madison,Wis.; Stratagene; La Jolla, Calif.; Amersham; Arlington Heights, Ill.;GIBCO/BRL; Grand Island, N.Y.). Membranous extracts, such as the caninepancreatic extracts containing microsomal membranes, are also availablewhich are useful for translating secretory proteins. Mixtures ofpurified translation factors have also been used successfully totranslate mRNA into protein as well as combinations of lysates orlysates supplemented with purified translation factors such asinitiation factor-1 (IF-1), IF-2, IF-3 (α or β), elongation factor T(EF-Tu), or termination factors.

Cell-free systems may also be coupled transcription/translation systemswherein DNA is introduced to the system, transcribed into mRNA and themRNA translated as described in Current Protocols in Molecular Biology(F. M. Ausubel et al. editors, Wiley Interscience, 1993), which ishereby specifically incorporated by reference. RNA transcribed ineukaryotic transcription system may be in the form of heteronuclear RNA(hnRNA) or 5′-end caps (7-methyl guanosine) and 3′-end poly A tailedmature mRNA, which can be an advantage in certain translation systems.For example, capped mRNAs are translated with high efficiency in thereticulocyte lysate system.

tRNA molecules chosen for misaminoacylation with marker do notnecessarily possess any special properties other than the ability tofunction in the protein synthesis system. Due to the universality of theprotein translation system in living systems, a large number of tRNAscan be used with both cellular and cell-free reaction mixtures. SpecifictRNA molecules which recognize unique codons, such as nonsense or ambercodons (UAG), are not required.

Site-directed incorporation of the nonnative analogs into the proteinduring translation is also not required. Incorporation of markers canoccur anywhere in the polypeptide and can also occur at multiplelocations. This eliminates the need for prior information about thegenetic sequence of the translated mRNA or the need for modifying thisgenetic sequence.

In some cases, it may be desirable to preserve the functional propertiesof the nascent protein. A subset of tRNAs which will incorporate markersat sites which do not interfere with protein function or structure canbe chosen. Amino acids at the amino or carboxyl terminus of apolypeptide do not alter significantly the function or structure. tRNAmolecules which recognize the universal codon for the initiation ofprotein translation (AUG), when misaminoacylated with marker, will placemarker at the amino terminus. Prokaryotic protein synthesizing systemsutilize initiator tRNA^(fMet) molecules and eukaryotic systems initiatortRNA^(Met) molecules. In either system, the initiator tRNA molecules areaminoacylated with markers which may be non-native amino acids or aminoacid analogs or derivatives that possess marker, reporter or affinityproperties. The resulting nascent proteins will be exclusively labeledat their amino terminus, although markers placed internally do notnecessarily destroy structural or functional aspects of a protein. Forexample, a tRNA^(LYS) may be misaminoacylated with the amino acidderivative dansyllysine which does not interfere with protein functionor structure. In addition, using limiting amounts of misaminoacylatedtRNAs, it is possible to detect and isolate nascent proteins having onlya very small fraction labeled with marker which can be very useful forisolating proteins when the effects of large quantities of marker wouldbe detrimental or are unknown.

tRNAs molecules used for aminoacylation are commercially available froma number of sources and can be prepared using well-known methods fromsources including Escherichia coli, yeast, calf liver and wheat germcells (Sigma Chemical; St. Louis, Mo.; Promega; Madison, Wis.;Boehringer Mannheim Biochemicals; Indianapolis, Ind.). Their isolationand purification mainly involves cell-lysis, phenol extraction followedby chromatography on DEAE-cellulose. Amino-acid specific tRNA, forexample tRNA^(fMet), can be isolated by expression from cloned genes andoverexpressed in host cells and separated from total tRNA by techniquessuch as preparative polyacrylamide gel electrophoresis followed by bandexcision and elution in high yield and purity (Seong and RajBhandary,Proc. Natl. Acad. Sci. USA 84:334-338, 1987). Run-off transcriptionallows for the production of any specific tRNA in high purity, but itsapplications can be limited due to lack of post-transcriptionalmodifications (Bruce and Uhlenbeck, Biochemistry 21:3921, 1982).

Misaminoacylated tRNAs are introduced into the cellular-or cell-freeprotein synthesis system. In the cell-free protein synthesis system, thereaction mixture contains all the cellular components necessary tosupport protein synthesis including ribosomes, tRNA, rRNA, spermidineand physiological ions such as magnesium and potassium at appropriateconcentrations and an appropriate pH. Reaction mixtures can be normallyderived from a number of different sources including wheat germ, E. coli(S-30), red blood cells (reticulocyte lysate,) and oocytes, and oncecreated can be stored as aliquots at about +4° C. to −70° C. The methodof preparing such reaction mixtures is described by J. M. Pratt(Transcription and Translation, B. D. Hames and S. J. Higgins, Editors,p. 209, IRL Press, Oxford, 1984) which is hereby incorporated byreference. Many different translation systems are commercially availablefrom a number of manufacturers.

The misaminoacylated tRNA is added directly to the reaction mixture as asolution of predetermined volume and concentration. This can be donedirectly prior to storing the reaction mixture at −70° C. in which casethe entire mixture is thawed prior to initiation of protein synthesis orprior to the initiation of protein synthesis. Efficient incorporation ofmarkers into nascent proteins is sensitive to the final pH and magnesiumion concentration. Reaction mixtures are normally about pH 6.8 andcontain a magnesium ion concentration of about 3 mM. These conditionsimpart stability to the base-labile aminoacyl linkage of themisaminoacylated tRNA. Aminoacylated tRNAs are available in sufficientquantities from the translation extract. Misaminoacylated tRNAs chargedwith markers are added at between about 1.0 μg /ml to about 1.0 mg/ml,preferably at between about 10 μg/ml to about 500 and more preferably atabout 150 μg/ml.

Initiation of protein synthesis occurs upon addition of a quantity ofmRNA or DNA to the reaction mixture containing the misaminoacylatedtRNAs. mRNA molecules may be prepared or obtained from recombinantsources, or purified from other cells by procedure such as poly-dTchromatography. One method of assuring that the proper ratio of thereaction mixture components is to use predetermined volumes that arestored in convenient containers such as vials or standardmicrocentrifuge tubes. For example, DNA and/or mRNA coding for thenascent proteins and the misaminoacylated tRNA solution are premixed inproper amounts and stored separately in tubes. Tubes are mixed whenneeded to initiate protein synthesis.

Translations in cell-free systems generally require incubation of theingredients for a period of time. Incubation times range from about 5minutes to many hours, but is preferably between about thirty minutes toabout five hours and more preferably between about one to about threehours. Incubation may also be performed in a continuous manner wherebyreagents are flowed into the system and nascent proteins removed or leftto accumulate using a continuous flow system (A. S. Spirin et al., Sci.242:1162-64, 1988). This process may be desirable for large scaleproduction of nascent proteins. Incubations may also be performed usinga dialysis system where consumable reagents are available for thetranslation system in an outer reservoir which is separated from largercomponents of the translation system by a dialysis membrane [Kim, D.,and Choi, C. (1996) Biotechnol Prog 12, 645-649]. Incubation times varysignificantly with the volume of the translation mix and the temperatureof the incubation. Incubation temperatures can be between about 4° C. toabout 60° C., and are preferably between about 15° C. to about 50° C.,and more preferably between about 25° C. to about 45° C. and even morepreferably at about 25° C. or about 37° C. Certain markers may besensitive to temperature fluctuations and in such cases, it ispreferable to conduct those incubations in the non-sensitive ranges.Translation mixes will typically comprise buffers such as Tris-HCl,Hepes or another suitable buffering agent to maintain the pH of thesolution between about 6 to 8, and preferably at about 7. Again, certainmarkers may be pH sensitive and in such cases, it is preferable toconduct incubations outside of the sensitive ranges for the marker.Translation efficiency may not be optimal, but marker utility will beenhanced. Other reagents which may be in the translation system includedithiothreitol (DTT) or 2-mercaptoethanol as reducing agents, RNasin toinhibit RNA breakdown, and nucleoside triphosphates or creatinephosphate and creatine kinase to provide chemical energy for thetranslation process.

In cellular protein synthesis, it is necessary to introducemisaminoacylated tRNAs or markers into intact cells, cell organelles,cell envelopes and other discrete volumes bounded by an intactbiological membrane, which contain a protein synthesizing system. Thiscan be accomplished through a variety of methods that have beenpreviously established such as sealing the tRNA solution into liposomesor vesicles which have the characteristic that they can be induced tofuse with cells. Fusion introduces the liposome or vesicle interiorsolution containing the tRNA into the cell. Alternatively, some cellswill actively incorporate liposomes into their interior cytoplasmthrough phagocytosis. The tRNA solution could also be introduced throughthe process of cationic detergent mediated lipofection (Feigner et al.,Proc. Natl. Acad. Sci. USA 84:7413-17, 1987), or injected into largecells such as oocytes. Injection may be through direct perfusion withmicropipettes or through the method of electroporation.

Alternatively, cells can be permeabilized by incubation for a shortperiod of time in a solution containing low concentrations of detergentsin a hypotonic media. Useful detergents include Nonidet-P 40 (NP40),Triton X-100 (TX-100) or deoxycholate at concentrations of about 0.01 nMto 1.0 mM, preferably between about 0.1 μM to about 0.01 mM, and morepreferably about 1 μM. Permeabilized cells allow marker to pass throughcellular membranes unaltered and be incorporated into nascent proteinsby host cell enzymes. Such systems can be formed from intact cells inculture such as bacterial cells, primary cells, immortalized cell lines,human cells or mixed cell populations. These cells may, for example, betransfected with an appropriate vector containing the gene of interest,under the control of a strong and possibly regulated promoter. Messagesare expressed from these vectors and subsequently translated withincells. Intact misaminoacylated tRNA molecules, already charged with anon-radioactive marker could be introduced to cells and incorporatedinto translated product.

One example of the use of misaminoacylation to detect nascent protein isschematically represented in FIG. 4. A tRNA molecule is misaminoacylatedwith the marker which is highly fluorescent when excited with UV(ultraviolet) radiation. The misaminoacylated tRNA is then introducedinto a cell-free protein synthesis extract and the nascent proteinscontaining the marker analog produced. Proteins in the cell-free extractare separated by polyacrylamide gel electrophoresis (PAGE). Theresulting gel contains bands which correspond to all of the proteinspresent in the cell-free extract. The nascent protein is identified uponUV illumination of the gel by detection of fluorescence from the bandcorresponding to proteins containing marker. Detection can be throughvisible observation or by other conventional means of fluorescencedetection.

The misaminoacylated tRNA can be formed by natural aminoacylation usingcellular enzymes or misaminoacylation such as chemicalmisaminoacylation. One type of chemical misaminoacylation involvestruncation of the tRNA molecule to permit attachment of the marker ormarker precursor. For example, successive treatments with periodate pluslysine, pH 8.0, and alkaline phosphatase removes 3′-terminal residues ofany tRNA molecule generating tRNA-OH-3′ with a mononucleotide ordinucleotide deletion from the 3′-terminus (Neu and Heppel, 3. Biol.Chem. 239:2927-34, 1964). Alternatively, tRNA molecules may begenetically manipulated to delete specific portions of the tRNA gene.The resulting gene is transcribed producing truncated tRNA molecules(Sampson and Uhlenbeck, Proc. Natl. Acad. Sci. USA 85:1033-37, 1988).Next, a dinucleotide is chemically linked to a modified amino acid orother marker by, for example, acylation. Using this procedure, markerscan be synthesized and acylated to dinucleotides in high yield (Hudson,J. Org. Chem. 53:617-624, 1988; Happ et al., J. Org. Chem. 52:5387-91,1987). These modified groups are bound together and linked via thedinucleotide to the truncated tRNA molecules in a process referred to asligase coupling (FIG. 3B).

A different bond is involved in misaminoacylation (FIG. 3B, link B) thanthe bond involved with activation of tRNA by aminoacyl tRNA synthetase(FIG. 3B, link A). As T4 RNA ligase does not recognize the acylsubstituent, tRNA molecules can be readily misaminoacylated with fewchemical complications or side reactions (link B, FIG. 3B) (T. G.Heckler et al., Biochemistry 23:1468-73, 1984; and T. G. Heckler et al.,Tetrahedron 40:87-94, 1984). This process is insensitive to the natureof the attached amino acid and allows for misaminoacylation using avariety of non-native amino acids. In contrast, purely enzymaticaminoacylation (link A) is highly sensitive and specific for thestructures of substrate tRNA and amino acids.

Markers are basically molecules which will be recognized by the enzymesof the translation process and transferred from a charged tRNA into agrowing peptide chain. To be useful, markers must also possess certainphysical and physio-chemical properties. Therefore, there are multiplecriteria which can be used to identify a useful marker. First, a markermust be suitable for incorporation into a growing peptide chain. Thismay be determined by the presence of chemical groups which willparticipate in peptide bond formation. Second, markers should beattachable to a tRNA molecule. Attachment is a covalent interactionbetween the 3′-terminus of the tRNA molecule and the carboxy group ofthe marker or a linking group attached to the marker and to a truncatedtRNA molecule. Linking groups may be nucleotides, short oligonucleotidesor other similar molecules and are preferably dinucleotides and morepreferably the dinucleotide CA. Third, markers should have one or morephysical properties that facilitate detection and possibly isolation ofnascent proteins. Useful physical properties include a characteristicelectromagnetic spectral property such as emission or absorbance,magnetism, electron spin resonance, electrical capacitance, dielectricconstant or electrical conductivity.

Useful markers are native amino acids coupled with a detectable label,detectable non-native amino acids, detectable amino acid analogs anddetectable amino acid derivatives. Labels and other detectable moietiesmay be ferromagnetic, paramagnetic, diamagnetic, luminescent,electrochemiluminescent, fluorescent, phosphorescent, chromatic or havea distinctive mass. Fluorescent moieties which are useful as markersinclude dansyl fluorophores, coumarins and coumarin derivatives,fluorescent acridinium moieties and benzopyrene based fluorophores.Preferably, the fluorescent marker has a high quantum yield offluorescence at a wavelength different from native amino acids and morepreferably has high quantum yield of fluoresence can be excited in boththe UV and visible portion of the spectrum. Upon excitation at apreselected wavelength, the marker is detectable at low concentrationseither visually or using conventional fluorescence detection methods.Electrochemiluminescent markers such as ruthenium chelates and itsderivatives or nitroxide amino acids and their derivatives are preferredwhen extreme sensitivity is desired (J. DiCesare et al., BioTechniques15:152-59, 1993). These markers are detectable at the femtomolar rangesand below.

In addition to fluorescent markers, a variety of markers possessingother specific physical properties can be used to detect nascent proteinproduction. In general, these properties are based on the interactionand response of the marker to electromagnetic fields and radiation andinclude absorption in the UV, visible and infrared regions of theelectromagnetic spectrum, presence of chromophores which are Ramanactive, and can be further enhanced by resonance Raman spectroscopy,electron spin resonance activity and nuclear magnetic resonances and useof a mass spectrometer to detect presence of a marker with a specificmolecular mass. These electromagnetic spectroscopic properties arepreferably not possessed by native amino acids or are readilydistinguishable from the properties of native amino acids. For example,the amino acid tryptophan absorbs near 290 nm, and has fluorescentemission near 340 nm when excited with light near 290 nm. Thus,tryptophan analogs with absorption and/or fluorescence properties thatare sufficiently different from tryptophan can be used to facilitatetheir detection in proteins.

Many different modified amino acids which can be used as markers arecommercially available (Sigma Chemical; St. Louis, Mo.; MolecularProbes; Eugene, Oreg.). One such marker is Nε-dansyllysine created bythe misaminoacylation of a dansyl fluorophore to a tRNA molecule (FIG.5; scheme 1). The α-amino group of Nε-dansyllysine is first blocked withNVOC (ortho-nitro veratryl oxycarbonyl chloride) and the carboxyl groupactivated with cyanomethyl ester. Misaminoacylation is performed asdescribed. The misaminoacylated tRNA molecules are then introduced intothe protein synthesis system, whereupon the dansyllysine is incorporateddirectly into the newly synthesized proteins.

Another such marker is a fluorescent amino acid analog based on thehighly fluorescent molecule coumarin (FIG. 5; scheme 2). Thisfluorophore has a much higher fluorescence quantum yield than dansylchloride and can facilitate detection of much lower levels of nascentprotein. In addition, this coumarin derivative has a structure similarto the native amino acid tryptophan. These structural similarities areuseful where maintenance of the nascent proteins' native structure orfunction are important or desired. Coumarin is synthesized as depictedin FIG. 5 (scheme 2). Acetamidomalonate is alkylated with a slightexcess of 4-bromomethyl coumarin (Aldrich Chemicals; Milwaukee; Wis.) inthe presence of sodium ethoxide followed by acid hydrolysis. Thecorresponding amino acid as a hydrochloride salt that can be convertedto the free amino acid analog.

The coumarin derivative can be used most advantageously if itmisamino-acylates the tryptophan-tRNA, either enzymatically orchemically. When introduced in the form of the misaminoacylatedtryptophan-tRNA, the coumarin amino acid will be incorporated only intotryptophan positions. By controlling the concentration ofmisaminoacylated tRNAs or free coumarin derivatives in the cell-freesynthesis system, the number of coumarin amino acids incorporated intothe nascent protein can also be controlled. This procedure can beutilized to control the amount of most any markers in nascent proteins.

Markers can be chemically synthesized from a native amino acid and amolecule with marker properties which cannot normally function as anamino acid. For example a highly fluorescent molecule can be chemicallylinked to a native amino acid group. The chemical modification can occuron the amino acid side-chain, leaving the carboxyl and aminofunctionalities free to participate in a polypeptide bond formation.Highly fluorescent dansyl chloride can be linked to the nucleophilicside chains of a variety of amino acids including lysine, arginine,tyrosine, cysteine, histidine, etc., mainly as a sulfonamide for aminogroups or sulfate bonds to yield fluorescent derivatives. Suchderivatization leaves the ability to form peptide bond intact, allowingthe normal incorporation of dansyllysine into a protein.

A number of factors determine the usefulness of a marker which is to beincorporated into nascent proteins through misaminoacylated tRNAs. Theseinclude the ability to incorporate the marker group into the proteinthrough the use of a misaminoacylated tRNA in a cell-free or cellularprotein synthesis system and the intrinsic detectability of the markeronce it is incorporated into the nascent protein. In general, markerswith superior properties will allow shorter incubation times and requiresmaller samples for the accurate detection of the nascent proteins.These factors directly influence the usefulness of the methodsdescribed. In the case of fluorescent markers used for the incorporationinto nascent proteins, favorable properties can be but are not limitedto, small size, high quantum yield of fluorescence, and stability toprolonged light exposure (bleach resistance).

Even with knowledge of the above factors, the ability to incorporate aspecific marker into a protein using a specific cell-free or cellulartranslation system is difficult to determine a priori since it dependson the detailed interaction of the marker group with components of theprotein translational synthesis system including the tRNA, initiation orelongation factors and components of the ribosome. While it is generallyexpected that markers with smaller sizes can be accommodated morereadily into the ribosome, the exact shape of the molecule and itsspecific interactions in the ribosomal binding site will be the mostimportant determinant. For this reason, it is possible that some markerswhich are larger in size can be more readily incorporated into nascentproteins compared to smaller markers. For example, such factors are verydifficult to predict using known methods of molecular modeling.

One group of fluorophores with members possessing several favorableproperties (including favorable interactions with components of theprotein translational synthesis system) is the group derived fromdipyrrometheneboron difluoride derivatives (BODIPY) (FIG. 19). Comparedto a variety of other commonly used fluorophores with advantageousproperties such as high quantum yields, some BODIPY compounds have theadditional unusual property that they are highly compatible with theprotein synthesis system. The core structure of all BODIPY fluorophoresis 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. See U.S. Pat. Nos.4,774,339; 5,187,288;5,248,782; 5,274,113;5,433,896; 5,451,663, allhereby incorporated by reference. A central feature is a difluoroboronas shown in FIG. 19. All BODIPY fluorophores have several desirableproperties for a marker (Molecular Probes Catalog, pages 13-18)including a high extinction coefficient, high fluorescence quantumyield, spectra that are insensitive to solvent polarity and pH, narrowemission bandwidth resulting in a higher peak intensity compared toother dyes such as fluoresceins, absence of ionic charge and enhancedphotostability compared to fluorosceine. The addition of substituents tothe basic BODIPY structure which cause additional conjugation can beused to shift the wavelength of excitation or emission to convenientwavelengths compatible with the means of detection.

These dyes were described for the first time by Vos de Waal et al.(1977) and its fluorescence properties subsequently described by Wories[See Wories et al., “A novel water-soluble fluorescent probe: Synthesis,luminescence and biological properties of the sodium salt of the4-sulfonato-3,3′,5′5-tetramethyl-2,2′-pyrromethen-1,1′-BF.sub.2complex,” Recl. Trav. Chim. PAYSBAS 104, 288 (1985). Dyes derived fromdipyrrometheneboron difluoride have additional characteristics that makethem suitable for incorporation into nascent proteins. Simple alkylderivatives of the fluorophore4,4-difluoro-4-bora-3a,4a-diaza-s-indacene have been described by Treibs& Kreuzer, [Difluorboryl-komplexe von di- and tripyrrylmethenen, LIEBIGSANNALEN CHEM. 718,208 (1968)] and by Worries, Kopek, Lodder, &Lugtenburg, [A novel water-soluble fluorescent probe: Synthesis,luminescence and biological properties of the sodium salt of the4-sulfonato-3,3′,5,5′-tetramethyl-2,2′-pyrromethen-1,1-BF.sub.2 complex,RECL. TRAY. CHIM. PAYS-BAS 104, 288 (1985)] as being highly fluorescentwith spectral properties that are similar to fluorescein, with maximumabsorbance at about 490 to 510 nm and maximum emission at about 500 to530 nm. U.S. Pat. No. 4,774,339 to Haugland et al. (1988) ('339 patent)(hereby incorporated by reference) describes4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (dipyrrometheneborondifluoride) dyes including hydrogen, halogen, alkyl, cycloalkyl, aryl,arylalkyl, acyl, and sulfo-substituted derivatives that contain reactivegroups suitable for conjugation to biomolecules, that have goodphotostability, and which have fluorescein-like spectra. As described inthe '339 patent, and by Pavlopoulos, et al., [Laser action from atetramethylpyrromethene-BF.sub.2 complex, APP. OPTICS 27, 4998 (1988)],the emission of the alkyl derivatives of4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorescent dyes clearlyoverlaps that of fluorescein. The overlap allows the alkyl derivativesof dipyrrometheneboron difluoride to be used with the same opticalequipment as used with fluorescein-based dyes without modification ofthe excitation sources or optical filters. Similarly, aryl/heteroarylsubstituents in the dipyrrometheneboron difluoride cause the maximum ofabsorbance/emission to shift into longer wavelengths (See U.S. Pat. No.5,451,663 hereby incorporated by reference).

A variety of BODIPY molecules are commercially available in an aminereactive form which can be used to derivitize aminoacylated tRNAs toyield a misaminoacylated tRNA with a BODIPY marker moiety. One exampleof a compound from this family which exhibits superior properties forincorporation of a detectable marker into nascent proteins is4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY-FL).When the sulfonated N-hydroxysuccinimide (NHS) derivative of BODIPY-FLis used to misaminoacylate an E. coli initiator tRNA^(fmet), the nascentprotein produced can be easily detected on polyacyrlamide gels afterelectrophoresis using a standard UV-transilluminator and photographic orCCD imaging system. This can be accomplished by using purifiedtRNA^(fmet) which is first aminoacylated with methionine and then theα-amino group of methionine is specifically modified usingN-hydroxysuccinimide BODIPY. Before the modification reaction, thetRNA^(fmet) is charged maximally (>90%) and confirmed by using³⁵S-methionine and acid-urea gels [Varshney, U., Lee, C. P., andRajBhandary, U. L. 1991. Direct analysis of aminoacylation levels oftRNA in vitro. J. Biol. Chem 266:24712-24718].

Less than 10 nanoliters of a commercially available E.coli extract (E.coli T7 translation system, Promega, Madison, Wis.) are needed foranalysis corresponding to less than 1 ng of synthesized protein.Incubation times required to produce detectable protein is approximately1 hour but can be as little as 5 minutes. BODIPY-FL can also be detectedwith higher sensitivity using commercially available fluorescentscanners with 488 nm excitation and emission measurement above 520 nm.Similar tests using other commercially available dyes including NBD(7-Nitrobenz-2-Oxa-1,3-Diazole), and Pyrine-PyMPO show approximately anorder of magnitude reduction in fluorescence making them difficult todetect using standard laboratory equipment such as a UV-transilluminatoror fluorescent scanner. It has previously been shown that fluorescentmarkers such as3-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-2,3,-diaminoproprionic acid(NBD-DAP) and coumarin could be incorporated into proteins usingmisaminoacylated tRNAs. However, detection of nascent proteinscontaining these markers was only demonstrated using highly sensitiveinstrumentation such a fluorescent spectrometer or amicrospectrofluorimeter and often require indirect methods such as theuse of fluorescence resonance energy transfer (FRET) (Turcatti, G.,Nemeth, K., Edgerton, M. D., Meseth, U., Talabot, F., Peitsch, M.,Knowles, J., Vogel, H., and Chollet, A. (1996) J Biol Chem 271(33),19991-8; Kudlicki, W., Odom, O. W., Kramer, G., and Hardesty, B. (1994)J Mol Biol 244(3), 319-31). Such instruments are generally not availablefor routine use in a molecular biology laboratory and only with specialadaptation can be equipped for measurement of fluorescent bands on agel.

An additional advantage of BODIPY-FL as a marker is the availability ofmonoclonal antibodies directed against it which can be used to affinitypurify nascent proteins containing said marker. One example of such amonoclonal antibody is anti-BODIPY-FL antibody (Cat# A-5770, MolecularProbes, Eugene, Oreg.). This combined with the ability incorporateBODIPY-FL into nascent proteins with high efficiency relative to othercommercially available markers using misaminoacylated tRNAs facilitatesmore efficient isolation of the nascent protein. These antibodiesagainst BODIPY-FL can be used for quantitation of incorporation of theBODIPY into the nascent protein.

A marker can also be modified after the tRNA molecule is aminoacylatedor misaminoacylated using chemical reactions which specifically modifythe marker without significantly altering the functional activity of theaminoacylated tRNA. These types of post-aminoacylation modifications mayfacilitate detection, isolation or purification, and can sometimes beused where the modification allow the nascent protein to attain a nativeor more functional configuration.

Fluorescent and other markers have detectable electromagnetic spectralproperties that can be detected by spectrometers and distinguished fromthe electromagnetic spectral properties of native amino acids.Spectrometers which are most useful include fluorescence, Raman,absorption, electron spin resonance, visible, infrared and ultravioletspectrometers. Other markers, such as markers with distinct electricalproperties can be detected by an apparatus such as an ammeter, voltmeteror other spectrometer. Physical properties of markers which relate tothe distinctive interaction of the marker with an electromagnetic fieldis readily detectable using instruments such as fluorescence, Raman,absorption, electron spin resonance spectrometers. Markers may alsoundergo a chemical, biochemical, electrochemical or photochemicalreaction such as a color change in response to external forces or agentssuch as an electromagnetic field or reactant molecules which allows itsdetection.

One class of fluorescent markers contemplated by the present inventionis the class of small peptides that can specifically bind to moleculeswhich, upon binding, are detectable. One example of this approach is thepeptide having the sequence of WEAAAREACCRECCARA. This sequence (whichcontains four cysteine residues) allows the peptide to specifically bindthe non-fluorescent dye molecule 4′,5′-bis(1,3,2-dithioarsolan-2-yl)fluorescein (FLASH, which stands for fluorescein arsenic helix binder).This dye has the interesting property that, upon binding, it becomesfluorescent. In other words, fluorescence is observed only when thisspecific peptide sequence is present in the nascent protein. So byputting the peptide sequence at the N- or C-terminal, one can easilymonitor the amount of protein synthesized. This peptide sequence can beintroduced by designing the nucleic acid primers such that they carry aregion encoding the peptide sequence.

Regardless of which class of fluorescent compounds is used, detectionnormally first involves physical separation of the nascent proteins fromother biomolecules present in the cellular or cell-free proteinsynthesis system. Protein separation can be performed using, forexample, gel electrophoresis or column chromatography and can be furtherfacilitated with affinity markers which uniquely bind acceptor groups.Detection of a marker containing a fluorophore by gel electrophoresiscan be accomplished using conventional fluorescence detection methods.

After protein synthesis in a cell-free system, the reaction mixture,which contains all of the biomolecules necessary for protein synthesisas well as nascent proteins, is loaded onto a gel which may be composedof polyacrylamide or agarose (R. C. Allen et al., Gel Electrophoresisand Isoelectric Focusing of Proteins, Walter de Gruyter, New York 1984).This mixture also contains the misaminoacylated tRNAs bearing the markeras well as uncharged tRNAs. Subsequent to loading the reaction mixture,a voltage is applied which spatially separates the proteins on the gelin the direction of the applied electric field. The proteins separateand appear as a set of discrete or overlapping bands which can bevisualized using a pre- or post-gel staining technique such as Coomasieblue staining. The migration of the protein band on the gel is afunction of the molecular weight of the protein with increasing distancefrom the loading position being a function of decreasing molecularweight. Bands on the gel which contain nascent proteins will exhibitfluorescence when excited at a suitable wavelength. These bands can bedetected visually, photographically or spectroscopically and, ifdesired, the nascent proteins purified from gel sections.

For example, if BODIPY-FL is used as a marker, nascent proteins willfluoresce at 510 nm when excited by UV illumination. This fluorescencecan be detected visually by simply using a standard hand-held UVilluminator or a transilluminator. Approximately 10 nanograms (ng) ofthe protein alpha-hemolysin is detectable using this method. Also usefulare electronic imaging devices which can rapidly screen and identifyvery low concentrations of markers such as a fluorescent scanner basedon a low-temperature CCD imager. In this case as low as 0.3 ng ofprotein can be detected.

The molecular weight and quantity of the nascent protein can bedetermined by comparison of its band-position on the gel with a set ofbands of proteins of predetermined molecular weight which arefluorescently labeled. For example, a nascent protein of molecularweight 25,000 could be determined because of its relative position onthe gel relative to a calibration gel containing the commerciallyavailable standard marker proteins of known quantities and with knownmolecular weights (bovine serum albumin, 66 kD; porcine heart fumarase,48.5 kD; carbonic anhydrase, 29 kD, β-lactoglobulin, 18.4 kD;α-lactoglobulin, 14.2 kD; Sigma Chemical; St. Louis, Mo.).

Calibration proteins may also contain a similar markers for convenientdetection using the same method as the gel bearing the nascent protein.This can be accomplished in many cases by directly reacting thecalibration proteins with a molecule similar to the marker. For example,the calibration proteins can be modified with dansyl chloride so as toobtain their fluorescent derivatives (R. E. Stephens, Anal. Biochem. 65,369-79, 1975). Alternatively, the proteins could be labeled with an NHSderivitive of BODIPY-FL. These fluorescent proteins can be analyzedusing PAGE. Combined detection of these fluorescent calibration proteinsalong with that of nascent protein which contains fluorescent markeranalog will accurately determine both the molecular weight and quantityof the nascent protein synthesized. If necessary, the amounts of markerwithin each calibration and nascent protein can be determined to providean accurate quantitation. Proteins with predetermined levels offluorescent markers can be used advantageously to provide forquantitation of the gel bearing the nascent protein. This could beaccomplished by genetically engineering a calibration protein so that itcontains a specific reactive residue such as cysteine so that only onefluorescent dye will be attached per protein.

Other methods of protein separation are also useful for detection andsubsequent isolation and purification of nascent proteins containingmarkers. For example, proteins can be separated using capillaryelectrophoresis, isoelectric focusing, low pressure chromatography andhigh-performance or fast-pressure liquid chromatography (HPLC or FPLC).In these cases, the individual proteins are separated into fractionswhich can be individually analyzed by fluorescent detectors at theemission wavelengths of the markers. Alternatively, on-line fluorescencedetection can be used to detect nascent proteins as they emerge from thecolumn fractionation system. A graph of fluorescence as a function ofretention time provides information on both the quantity and purity ofnascent proteins produced.

Another embodiment of the invention is directed to a method forlabeling, detecting and, if desired, isolating and purifying nascentproteins, as described above, containing cleavable markers. Cleavablemarkers comprise a chemical structure which is sensitive to externaleffects such as physical or enzymatic treatments, chemical or thermaltreatments, electromagnetic radiation such as gamma rays, x-rays,ultraviolet light, visible light, infrared light, microwaves, radiowaves or electric fields. The marker is aminoacylated to tRNA moleculesas before using conventional technology or misaminoacylated and added toa translation system. After incubation and production of nascentproteins, marker can be cleaved by the application of specifiedtreatments and nascent proteins detected. Alternatively, nascentproteins may also be detected and isolated by the presence or absence ofthe cleaved marker or the chemical moiety removed from the marker.

One example of a cleavable marker is a photocleavable marker such aschemical compounds which contain the 2-nitrobenzyl moiety (FIG. 6A).Upon illumination, these aromatic nitro compounds undergo an internaloxidation-reduction reaction (Pillai, Synthesis 1-26, 1980; Patchorniket al., J. Am. Chem. Soc. 92:6333-35, 1970). As a result, the nitrogroup is reduced to a nitroso group and an oxygen is inserted into thebenzylic carbon-hydrogen bond at the ortho position. The primaryphotochemical process is the intramolecular hydrogen abstraction by theexcited nitro group. This is followed by an electron-redistributionprocess to the aci-nitro form which rearranges to the nitroso product.Subsequent thermal reaction leads to the cleavage of substrate from thenitrobenzyl linkage (FIG. 6B). Examples of other cleavable markers areshown in FIG. 7.

It may sometimes be desirable to create a distance between the substrateand the cleavable moiety. To accomplish this, cleavable moieties may beseparated from substrates by cross-linker arms. Cross-linkers increasesubstrate access and stabilize the chemical structure, and can beconstructed using, for example, long alkyl chains or multiple repeatunits of caproyl moieties linked via amide linkages.

There are as many methods to synthesize cleavable markers as there aredifferent markers. One example for the synthesis of photocleavablebiotins based on nitrobenzyl alcohols involves four major steps.2-bromo-2′-nitroacetphenone, a precursor of the photoreactive moiety, isfirst converted into an α- or ω-amino acid like ε-aminocaprylic acid.The resulting acid and amino functionality of the photoreactive group iscoupled using dicyclohexyl carbodiimide (DCC). The benzoyl carbonylgroup of the resulting amide is reduced using sodium borohydride. Theresulting derivative of nitrobenzyl alcohol is derivatized to obtain thefinal component which is able to react with biomolecular substrates, forexample by the reaction with phosgene gas, to introduce thechloroformate functionality. The resulting compound is depicted in FIG.8A along with alternative derivatives of PCB. Possible linkages to aminoacids are depicted in FIG. 8B.

Cleavable markers can facilitate the isolation of nascent proteins. Forexample, one type of a cleavable marker is photocleavable biotin coupledto an amino acid. This marker can be incorporated into nascent proteinsand the proteins purified by the specific interaction of biotin withavidin or streptavidin. Upon isolation and subsequent purification, thebiotin is removed by application of electromagnetic radiation andnascent proteins utilized in useful applications without thecomplications of an attached biotin molecule. Other examples ofcleavable markers include photocleavable coumarin, photocleavabledansyl, photocleavable dinitrophenyl and photocleavable coumarin-biotin.Photocleavable markers are cleaved by electromagnetic radiation such asUV light, peptidyl markers are cleaved by enzymatic treatments, andpyrenyl fluorophores linked by disulfide bonds are cleaved by exposureto certain chemical treatments such as thiol reagents.

Cleavage of photocleavable markers is dependent on the structure of thephotoreactive moiety and the wavelength of electromagnetic radiationused for illumination. Other wavelengths of electromagnetic radiationshould not damage the proteins or other chemical moieties. In the caseof unsubstituted 2-nitrobenzyl derivatives, the yield of photolysis andrecovery of the substrate are significantly decreased by the formationof side products which act as internal light filters and are capable toreact with amino groups of the substrate. Typical illumination timesvary from 1 to about 24 hours and yields are 1-95%. Radiation sourcesare placed within about 10 cm of the substrate proteins and set on lowpower so as to minimize side reactions, if any, which may occur in thenascent proteins. In the case of alpha-substituted 2-nitrobenzylderivatives (methyl, phenyl, etc.), a considerable increase in rate ofphoto-removal as well as yield of the released substrate are observed.The introduction of other electron donor groups into phenyl rings ofphotoreactive moieties increases the yield of substrate. The generalreaction for the photolysis of PCB is depicted in FIG. 9.

For enzymatic cleavage, markers introduced contain specific bonds whichare sensitive to unique enzymes of chemical substances. Introduction ofthe enzyme or chemical into the protein mixture cleaves the marker fromthe nascent protein. When the marker is a modified amino acid, this canresult in the production of native protein forms. Thermal treatments of,for example, heat sensitive chemical moieties operate in the samefashion. Mild application of thermal energy, such as with microwaves orradiant heat, cleaves the sensitive marker from the protein withoutproducing any significant damage to the nascent proteins.

Description of ?referred Embodiments A. Detection of Mutations

Detection of mutations is an increasingly important area in clinicaldiagnosis, including but not limited to the diagnosis of cancer and/orindividuals disposed to cancer. The protein truncation test (PTT) is atechnique for the detection of nonsense and frameshift mutations whichlead to the generation of truncated protein products. Genes associatedwith Duchenne muscular dystrophy, adenomatous polyposis coli, human mutLhomologue and human nutS homologue (both involved in colon cancer), andBRAC1 (involved in familial breast cancer) can now be screened formutations in this manner, along with others (see Table 1).

Typically, the PTT technique involves the incorproation of a T7 promotersite, ribosome binding site, and an artificial methionine start siteinto a PCR product covering the region of the gene to be investigated.The PCR product is then transcribed and translated using either an invitro rabbit reticulocyte lysate or wheat germ lysate system, togenerate a protein corresponding to the region of the gene amplified.The presence of a stop codon in the sequence, generated by a nonsensemutation or a frameshift, will result in the premature termination ofprotein translation, producing a truncated protein that can be detectedby standard gel electrophoresis (e.g. SDS-PAGE) analysis combined withradioactive dection.

There are drawbacks to the technique as currently practiced. One of themost important problems involves the identification of the product ofinterest. This is made difficult because of nonspecific radiolabeledproducts. Attempts to address these problems have been made. Oneapproach is to introduce an affinity tag after the start site and beforethe region encoding the gene of interest. See Rowan and Bodmer,“Introduction of a myc Reporter Tag to Improve the Quality of MutationDetection Using the Protein Truncation Test,” Human Mutation 9:172(1997). However, such approaches still have the disadvantage that theyrely on electrophoresis.

TABLE 1 Applications of PTT in Human Molecular Genetics % TruncatingDisease References Mutations Gene Familial Adenomatous 95% APC PolyposisHereditary desmold disease 100%  APC Ataxia telangiectasia 90% ATMHereditary Breast and 90% BRCA1 Ovarian Cancer 90% BRCA2 Cystic Fibrosis15% CFTR Duchenne Muscular 95% DMD Dystrophy Emery-Dreifuss Muscular 80%EMD Dystrophy Fanconi anaemia 80% FAA Hunter Syndrome −50%  IDSHereditary non-polyposis −80%  hMSH2 colorectal cancer −70%  hMLH1Neurofibromatosis type 1 50% NF1 Neurofibromatosis type 2 65% NF2Polycystic Kidney Disease 95% PKD1 Rubinstein-Taybi Syndrome 10% RTS Thepercentage of truncating mutations reported which should be detectableusing PTT.

The present invention contemplates a gel-free truncation test (GFTT),wherein two or three markers are introduced into the nascent protein.The present invention contemplates both pre-natal and post-natal testingto determine predisposition to disease. In a preferred embodiment of theinvention, the novel compositions and methods are directed to thedetection of frameshift or chain terminating mutations. In order todetect such mutations, a nascent protein is first synthesized in acell-free or cellular translation system from message RNA or DNA codingfor the protein which may contain a possible mutation. The nascentprotein is then separated from the cell-free or cellular translationsystem using an affinity marker located at or close to the N-terminalend of the protein. The protein is then analyzed for the presence of adetectable marker located at or close to the N-terminal of the protein(N-terminal marker). A separate measurement is then made on a sequencedependent detectable marker located at or close to the C-terminal end ofthe protein (C-terminal marker).

A comparison of the measurements from the C-terminal marker andN-terminal marker provides information about the fraction of nascentproteins containing frameshift or chain terminating mutations in thegene sequence coding for the nascent protein. The level of sequencedependent marker located near the C-terminal end reflects the fractionof protein which did not contain chain terminating or out-of-framemutations. The measurement of the N-terminal marker provides an internalcontrol to which measurement of the C-terminal marker is normalized.Normalizing the level of the C-terminal marker to the N-terminal markereliminates the inherent variabilities such as changes in the level ofprotein expression during translation that can undermine experimentalaccuracy. Separating the protein from the translation mixture using anusing an affinity marker located at or close to the N-terminal end ofthe protein eliminates the occurrence of false starts which can occurwhen the protein is initiated during translation from an internal AUG inthe coding region of the message. A false start can lead to erroneousresults since it can occurs after the chain terminating or out-of-framemutation. This is especially true if the internal AUG is in-frame withthe message. In this case, the peptide C-terminal marker will still bepresent even if message contains a mutation.

In one example, a detectable marker comprising a non-native amino acidor amino acid derivative is incorporated into the nascent protein duringits translation at the amino terminal (N-terminal end) using amisaminoacylate initiator tRNA which only recognizes the AUG start codonsignaling the initiation of protein synthesis. One example of adetectable marker is the highly fluorescent compound BODIPY FL. Themarker might also be photocleavable such as photocleavable coumarin orphotocleavable biotin. The nascent protein is then separated from thecell-free or cellular translation system by using a coupling agent whichbinds to an affinity marker located adjacent to the N-terminal of theprotein. One such affinity marker is a specific protein sequence knownas an epitope. An epitope has the property that it selectively interactswith molecules and/or materials containing acceptor groups. There aremany epitope sequences reported in the literature including His×6(HHHHHH) described by ClonTech and C-myc (-EQKLISEEDL) described byRoche-BM, Flag (DYKDDDDK) described by Stratagene), SteptTag (WSHPQFEK)described by Sigma-Genosys and HA Tag (YPYDVPDYA) described by Roche-BM.

Once the nascent protein is isolated from the translation system, it isanalyzed for presence of the detectable marker incorporated at theN-terminal of the protein. In the case of BODIPY FL, it can be detectedby measuring the level of fluorescence using a variety of commerciallyavailable instrument such as a Molecular Dynamics Model 595 fluorscencescanner that is equipped with excitation at 488 nm and an emissionfilter that allows light above 520 nm to be transmitted to the detector.

The protein is then analyzed for the presence of a sequence specificmarker located near the C-terminal end of the protein. In normalpractice, such a sequence specific marker will consist of a specificsequence of amino acids located near the C-terminal end of the proteinwhich is recognized by a coupling agent. For example, an antibody can beutilized which is directed against an amino acid sequence located at ornear C-terminal end of the nascent protein can be utilized. Suchantibodies can be labeled with a variety of markers including fluorscentdyes that can be easily detected and enzymes which catalzye detectablereactions that lead to easily detectable substrates. The marker chosenshould have a different detectable property than that used for theN-terminal marker. An amino acid sequence can also comprise an epitopewhich is recognized by coupling agents other than antibodies. One suchsequence is 6 histidines sometimes referred to as a his-tag which bindsto cobalt complex coupling agent.

A variety of N-terminal markers, affinity markers and C-terminal markersare available which can be used for this embodiment. The N-terminalmarker could be BODIPY, affinity marker could be StrepTag and C-terminalmarker could be a His×6 tag. In this case, after translation, thereaction mixture is incubated in streptavidin coated microtiter plate orwith streptavidin coated beads. After washing unbound material, theN-terminal marker is directly measured using a fluorescence scannerwhile the C-terminal marker can be quantitated using anti-his×6antibodies conjugated with a fluorescent dye (like rhodamine or TexasRed) which has optical properties different than BODIPY, thusfacilitating simultaneous dual detection.

In a different example, the N-terminal marker could be a biotin orphotocleavable biotin incorporated by a misaminoacylated tRNA, theaffinity marker could be a His ×6 tag and the C-terminal had C-mycmarker. In this case, after the translation, the reaction mixture isincubated with metal chelating beads or microtiter plates (for exampleTalon, ClonTech). After washing the unbound proteins, the plates orbeads can be subjected to detection reaction using streptavidineconjugated fluorescence dye and C-myc antibody conjugated with otherfluorescent dye. In addition, one can also use chemiluminescentdetection method using antibodies which are conjugated with peroxidases.

It will be understood by those skilled in the area of molecular biologyand biochemistry that the N-terminal marker, affinity marker andC-terminal marker can all consist of epitopes that can be incorporatedinto the nascent protein by designing the message or DNA coding for thenascent protein to have a nucleic acid sequence corresponding to theparticular epitope. This can be accomplished using known methods such asthe design of primers that incorporate the desired nucleic acid sequenceinto the DNA coding for the nascent protein using the polymerase chainreaction (PCR). It will be understood by those skilled in proteinbiochemistry that a wide variety of detection methods are available thatcan be used to detect both the N-terminal marker and the C-terminalmarkers. Additional examples include the use of chemiluminescence assayswhere an enzyme which converts a non-chemiluminescent substrate to achemiluminescent product is conjugated to an antibody that is directedagainst a particular epitope.

One example of this approach is based on using a luminometer to measureluminenscent markers. A biotin detectable marker is incorporated at theN-terminal using a misaminoacylated tRNA. The biotin is detected byusing a streptavidin which is conjugated to Renilla luciferase from seapansy. The C-terminal sequence comprises an epitope which interacts witha binding agent that has attached firefly luciferase. After separationof the nascent protein using a distinct epitope located near theN-terminal end of the protein, the protein is subjected to a dualluminescent luciferase assay based on a procedure described by PromegaCorp and known as the Dual-Luciferase® Reporter Assay. This assayconsists of first adding Luciferase Assay Reagent II available fromPromega Corp. to the isolated nascent protein and then measuring thelevel of chemiluminesence. Stop & Glo® Reagent is then added whichsimultaneously quenches the firefly luminescence and activates theRenilla luminescence. The luciferase assay can be performed andquantified in seconds. A comparison of the level of luminescencemeasured from the firefly and Renilla luciferase provides an indicationof whether a mutation is present or not in the coding message of thenascent protein.

In an additional example, the N-terminal marker comprises an affinitymarker which is incorporated at the N-terminal end of the protein duringits translation using a misaminoacylated tRNA. The affinity markerinteracts with a coupling agent which acts to separate the nascentprotein from the translation mixture. The nascent protein also containsa detectable marker which is located adjacent or close to the N-terminalof the protein containing the affinity marker. In addition, it containsa sequence specific marker at or near the C-terminal end of the protein.The detectable markers near the N-terminal and C-terminal ends of thenascent protein are then measured and compared to detect the presence ofchain terminating or out-of-frame mutations.

There are a variety of additional affinity markers, N-terminal markersand C-terminal markers available for this embodiment. The affinitymarker could be biotin or photocleavable biotin, N-terminal marker couldbe StepTag and C-terminal the C-myc epitope. In this case, after thetranslation, the reaction mixture is incubated with streptavidin coatedbeads or microtiter plates coated with streptavidin. After washing theunbound proteins, the plates or beads can be subjected to detectionreaction using anti-his 6 antibodies conjugated with a fluorescent dye(like rhodamine or Texas Red) and C-myc antibody conjugated with otheranother fluorescent dye such as BODIPY. In addition, one can also usechemiluminescent detection method using antibodies which are conjugatedwith peroxidases. Even in case of peroxidases conjugated antibodies, onecan use fluorescent substrates and use FluorImager like device toquantitate N-terminal and C-terminal labels.

For optimal effectiveness, the N-terminal marker and affinity markershould be placed as close as possible to the N-terminal end of theprotein. For example, if an N-terminal marker is incorporated using amisaminoacylated initiator, it will be located at the N-terminal aminoacid. In this case, the affinity marker should be located immediatelyadjacent to the N-terminal marker. Thus, if a BODIPY marker whichconsists of a BODIPY conjugated to methionine is incorporated by amisaminoacylated initiator tRNA, it should be followed by an epitopesequence such as SteptTag (WSHPQFEK) so that the entire N-terminalsequence will be BODIPY-MWSPQFEK. However, for specific cases it may beadvantageous to add intervening amino acids between the BODIPY-M and theepitope sequence in order to avoid interaction between the N-terminalmarker and the affinity marker or the coupling agent which binds theaffinity marker. Such interactions will vary depending on the nature ofthe N-terminal marker, affinity marker and coupling agent.

For optimal effectiveness, the C-terminal marker should be placed asclose as possible to the C-terminal end of protein. For example, if aHis-×6 tag is utilized, the protein sequence would terminate with 6 His.In some cases, an epitope may be located several residues before theC-terminal end of the protein in order to optimize the properties of thenascent protein. This might occur for example, if a specific amino acidsequence is necessary in order to modify specific properties of thenascent protein that are desirable such as its solubility orhydrophobicity.

In the normal application of this method, the ratio of the measuredlevel of N-terminal and C-terminal markers for a nascent proteintranslated from a normal message can be used to calculate a standardnormalized ratio. In the case of a message which may contain amutations, deviations from this standard ratio can then be used topredict the extent of mutations. For example, where all messages aredefective, the ratio of the C-terminal marker to the N-terminal markeris expected to be zero. On the other hand, in the case where allmessages are normal, the ratio is expected to be 1. In the case whereonly half of the message is defective, for example for a patient whichis heterozygote for a particular genetic defect which is chainterminating or causes an out-of-frame reading error, the ratio would be1/2.

There are several unique advantages of this method compared to existingtechniques for detecting chain terminating or out-of-frame mutations.Normally, such mutations are detected by analyzing the entire sequenceof the suspect gene using conventional DNA sequencing methods. However,such methods are time consuming, expensive and not suitable for rapidthroughput assays of large number of samples. An alternative method isto utilize gel electrophoresis, which is able to detect changes from theexpected size of a nascent protein. This approach, sometimes referred toas the protein truncation test, can be facilitated by usingnon-radioactive labeling methods such as the incorporation of detectablemarkers with misaminoacylated tRNAs. However, in many situations, suchas high throughput screening, it would be desirable to avoid the use ofgel electrophoresis which is time-consuming (typically 60-90 minutes).In the present method, the need for performing gel electrophoresis iseliminated. Furthermore, since the approach depends on comparison of twodetectable signals from the isolated nascent protein which can befluorscent, luminescent or some combination thereof, it is highlyamenable to automation.

Measuring a sequence dependent marker located near the C-terminal end ofthe protein provides information about the presence of either aframeshift or chain terminating mutation since the presence of eitherwould result in an incorrect sequence. The measurement of the N-terminalmarker provides an internal control to which measurement of theC-terminal marker is normalized. Normalizing the level of the C-terminalmarker to the N-terminal marker eliminates the inherent variabilitiessuch as changes in the level of protein expression during translationthat can undermine experimental accuracy. Separating the protein fromthe translation mixture using an using an affinity marker located at orclose to the N-terminal end of the protein eliminates the occurrence offalse starts which can occur when the protein is initiated duringtranslation from an internal AUG in the coding region of the message. Afalse start can lead to erroneous results since it can occurs after thechain terminating or out-of-frame mutation. This is especially true ifthe internal AUG is in-frame with the message. In this case, the peptideC-terminal marker will still be present even if message contains amutation.

B. Reporter Groups

Another embodiment of the invention is directed to a method formonitoring the synthesis of nascent proteins in a cellular or acell-free protein synthesis system without separating the components ofthe system. These markers have the property that once incorporated intothe nascent protein they are distinguishable from markers free insolution or linked to a tRNA. This type of marker, also called areporter, provides a means to detect and quantitate the synthesis ofnascent proteins directly in the cellular or cell-free translationsystem.

One type of reporters previously described in U.S. Pat. No. 5,643,722(hereby incorporated by reference) has the characteristic that onceincorporated into the nascent protein by the protein synthesizingsystem, they undergo a change in at least one of their physical orphysio-chemical properties. The resulting nascent protein can beuniquely detected inside the synthesis system in real time without theneed to separate or partially purify the protein synthesis system intoits component parts. This type of marker provides a convenientnon-radioactive method to monitor the production of nascent proteinswithout the necessity of first separating them from pre-existingproteins in the protein synthesis system. A reporter marker would alsoprovide a means to detect and distinguish between different nascentproteins produced at different times during protein synthesis byaddition of markers whose properties are distinguishable from eachother, at different times during protein expression. This would providea means of studying differential gene expression.

One example of the utilization of reporters is schematically representedin FIG. 10. A tRNA molecule is misaminoacylated with a reporter (R)which has lower or no fluorescence at a particular wavelength formonitoring and excitation. The misaminoacylated tRNA is then introducedinto a cellular or cell-free protein synthesis system and the nascentproteins containing the reporter analog are gradually produced. Uponincorporation of the reporter into the nascent protein (R*), it exhibitsan increased fluorescence at known wavelengths. The gradual productionof the nascent protein is monitored by detecting the increase offluorescence at that specific wavelength.

The chemical synthesis of a reporter can be based on the linkage of achemical moiety or a molecular component having reporter properties witha native amino acid residue. There are many fluorescent molecules whichare sensitive to their environment and undergo a change in thewavelength of emitted light and yield of fluorescence. When thesechemical moieties, coupled to amino acids, are incorporated into thesynthesized protein, their environments are altered because of adifference between the bulk aqueous medium and the interior of a proteinwhich can causes reduced accessibility to water, exposure to chargedionic groups, reduced mobility, and altered dielectric constant of thesurrounding medium. Two such examples are shown in FIG. 11A.

One example of a reporter molecule is based on a fluorescent acridiniummoiety and has the unique property of altering its emission properties,depending upon polarity or viscosity of the microenvironment. It has ahigher quantum yield of fluorescence when subjected to hydrophobicenvironment and/or viscosity. Due to the hydrophobicity of the reporteritself, it is more likely to be associated with the hydrophobic core ofthe nascent protein after incorporation into the growing nascentpolypeptide. An increase in the fluorescence intensity is a directmeasure of protein synthesis activity of the translation system.Although, the environment of each reporter residue in the protein willbe different, and in some cases, the reporter may be present on thesurface of the protein and exposed to an aqueous medium, a net changeoccurs in the overall spectroscopic properties of the reportersincorporated into the protein relative to bulk aqueous medium. A changein the spectroscopic properties of only a subset of reporters in theprotein will be sufficient to detect the synthesis of proteins thatincorporate such reporters.

An alternative approach is to utilize a reporter which alters itsfluorescent properties upon formation of a peptide bond and notnecessarily in response to changes in its environment. Changes in thereporter's fluorescence as it partitions between different environmentsin the cell-free extract does not produce a large signal change comparedto changes in fluorescence upon incorporation of the reporter into thenascent protein.

A second example of a reporter is a marker based on coumarin such as6,7-(4′, 5′-prolino)coumarin. This compound can be chemicallysynthesized by coupling a fluorophore like coumarin with an amino-acidstructural element in such a way that the fluorophore would alter itsemission or absorption properties after forming a peptide linkage (FIG.11B). For example, a proline ring containing secondary amino functionswill participate in peptide bond formation similar to a normal primaryamino group. Changes in fluorescence occur due to the co-planarity ofthe newly formed peptide group in relation to the existing fluorophore.This increases conjugation/delocalization due to the π-electrons ofnitrogen-lone pair and carbonyl-group in the peptide bond. Synthesis ofsuch compounds is based on on coumarin synthesis using ethylacetoacetate(FIG. 11C).

Reporters are not limited to those non-native amino acids which changetheir fluorescence properties when incorporated into a protein. Thesecan also be synthesized from molecules that undergo a change in otherelectromagnetic or spectroscopic properties including changes inspecific absorption bands in the UV, visible and infrared regions of theelectromagnetic spectrum, chromophores which are Raman active and can beenhanced by resonance Raman spectroscopy, electron spin resonanceactivity and nuclear magnetic resonances. In general, a reporter can beformed from molecular components which undergo a change in theirinteraction and response to electromagnetic fields and radiation afterincorporation into the nascent protein.

In the present invention, reporters may also undergo a change in atleast one of their physical or physio-chemical properties due to theirinteraction with other markers or agents which are incorporated into thesame nascent protein or are present in the reaction chamber in which theprotein is expressed. The interaction of two different markers with eachother causes them to become specifically detectable. One type ofinteraction would be a resonant energy transfer which occurs when twomarkers are within a distance of between about 1 angstrom (A) to about50 A, and preferably less than about 10 A. In this case, excitation ofone marker with electromagnetic radiation causes the second marker toemit electromagnetic radiation of a different wavelength which isdetectable. A second type of interaction would be based on electrontransfer between the two different markers which can only occur when themarkers are less than about 5 A. A third interaction would be aphotochemical reaction between two markers which produces a new speciesthat has detectable properties such as fluorescence. Although thesemarkers may also be present on the misaminoacylated tRNAs used for theirincorporation into nascent proteins, the interaction of the markersoccurs primarily when they are incorporated into protein due to theirclose proximity. In certain cases, the proximity of two markers in theprotein can also be enhanced by choosing tRNA species that will insertmarkers into positions that are close to each other in either theprimary, secondary or tertiary structure of the protein. For example, atyrosine-tRNA and a tryptophan-tRNA could be used to enhance theprobability for two different markers to be near each other in a proteinsequence which contains the unique neighboring pair tyrosine-tryptophan.

In one embodiment of this method, a reporter group is incorporated intoa nascent protein using a misaminoacylated tRNA so that when it binds toa coupling agent, the reporter group interacts with a second markers oragents which causes them to become specifically detectable. Such aninteraction can be optimized by incorporating a specific affinityelement into the nascent protein so that once it interacts with acoupling agent the interaction between the reporter group and the secondmarker is optimized. Such an affinity element might comprise a specificamino acid sequence which forms an epitope or a nonnative amino acid. Inone example, the reporter group is incorporated at the N-terminal of thenascent protein by using a misaminoacylated tRNA. The epitope isincorporated into the nascent protein so that when it interacts with thecoupling agent the reporter comes into close proximity with a secondmarker which is conjugated to the coupling agent.

One type of interaction between the markers that is advantageously usedcauses a fluorescence resonant energy transfer which occurs when the twomarkers are within a distance of between about 1 angstrom (A) to about50 A, and preferably less than about 10 A. In this case, excitation ofone marker with electromagnetic radiation causes the second marker toemit electromagnetic radiation of a different wavelength which isdetectable. This could be accomplished, for example, by incorporating afluorescent marker at the N-terminal end of the protein using the E.coli initiator tRNA^(fmet). An epitope is then incorporated near theN-terminal end such as the SteptTag (WSHPQFEK) described bySigma-Genosys. Streptavidin is then conjugated using known methods witha second fluorescent marker which is chosen to efficiently undergofluorescent energy transfer with marker 1. The efficiency of thisprocess can be determined by calculating the a Forster energy transferradius which depends on the spectral properties of the two markers. Themarker-streptavidin complex is then introduced into the translationmixture. Only when nascent protein is produced does fluorescent energytransfer between the first and second marker occur due to the specificinteraction of the nascent protein StreptTag epitope with thestreptavidin.

There are a variety of dyes which can be used as marker pairs in thismethod that will produce easily detectable signals when brought intoclose proximity. Previously, such dye pairs have been used for exampleto detect PCR products by hybridizing to probes labeled with a dye onone probe at the 5′-end and another at the 3′-end. The production of thePCR product brings a dye pair in close proximity causing a detectableFRET signal. In one application the dyes, fluoresein and LC 640 wereutilized on two different primers (Roche MolecularBiochemicals-http://www.biochem.boehringer-mannheim.com/lightcycler/monito03.htm).When the fluorescein is excited by green light (around 500 nm) that isproduced by a diode laser, the LC 640 emits red fluorescent light(around 640 nm) which can be easily detected with an appropriate filterand detector. In the case of nasent proteins, the pair of dyes BODIPY FLand LC 640 would function in a similar manner. For example,incorporation of the BODIPY FL on the N-terminal end of the protein andthe labeling of a binding agent with LC 640 which is directed against anN terminal epitope would allow detection of the production of nascentproteins.

The use of the marker pair BODIPY-FL and coumarin is a second pair whichcan be utilized advantageously. In one study, [Keller, R. C., Silvius,J. R., and De Kruijff, B. (1995) Biochem Biophys Res Commun 207(2),508-14] it was found using the spectral overlap a Forster energytransfer radius (RO) of 50 +/−2 A and 40 +/−2 A for the coumarin-beta-BODIPY FL) and the coumarin-(beta-BODIPY 530/550) couplerespectively. Experimentally this was estimated to be 49.0-51.5 A and38.5-42.5 A respectively. It is also possible to use two markers withsimilar or identical spectral properties for the marker pair due to theprocess of quenching. For example, in one study this process was used inthe case of BODIPY FL in order to study the processing of exogenousproteins in intact cells [Reis, R. C., Sorgine, M. H., andCoelho-Sampaio, T. (1998) Eur J Cell Biol 75(2), 192-7] and in a secondcase to study the kinetics of intracellular viral assembly [Da Poian, A.T., Games, A. M., and Coelho-Sampaio, T. (1998) J Virol Methods 70(1),45-58].

As stated above, a principal advantage of using reporters is the abilityto monitor the synthesis of proteins in cellular or a cell-freetranslation systems directly without further purification or isolationsteps. Reporter markers may also be utilized in conjunction withcleavable markers that can remove the reporter property at will. Suchtechniques are not available using radioactive amino acids which requirean isolation step to distinguish the incorporated marker from theunincorporated marker. With in vitro translation systems, this providesa means to determine the rate of synthesis of proteins and to optimizesynthesis by altering the conditions of the reaction. For example, an invitro translation system could be optimized for protein production bymonitoring the rate of production of a specific calibration protein. Italso provides a dependable and accurate method for studying generegulation in a cellular or cell-free systems.

C. Affinity Markers

Another embodiment of the invention is directed to the use of markersthat facilitate the detection or separation of nascent proteins producedin a cellular or cell-free protein synthesis system. Such markers aretermed affinity markers and have the property that they selectivelyinteract with molecules and/or materials containing acceptor groups. Theaffinity markers are linked by aminoacylation to tRNA molecules in anidentical manner as other markers of non-native amino acid analogs andderivatives and reporter-type markers as described. These affinitymarkers are incorporated into nascent proteins once the misaminoacylatedtRNAs are introduced into a translation system.

An affinity marker facilities the separation of nascent proteins becauseof its selective interaction with other molecules which may bebiological or non-biological in origin through a coupling agent. Forexample, the specific molecule to which the affinity marker interacts,referred to as the acceptor molecule, could be a small organic moleculeor chemical group such as a sulfhydryl group (—SH) or a largebiomolecule such as an antibody. The binding is normally chemical innature and may involve the formation of covalent or non-covalent bondsor interactions such as ionic or hydrogen bonding. The binding moleculeor moiety might be free in solution or itself bound to a surface, apolymer matrix, or a reside on the surface of a substrate. Theinteraction may also be triggered by an external agent such as light,temperature, pressure or the addition of a chemical or biologicalmolecule which acts as a catalyst.

The detection and/or separation of the nascent protein and otherpreexisting proteins in the reaction mixture occurs because of theinteraction, normally a type of binding, between the affinity marker andthe acceptor molecule. Although, in some cases some incorporatedaffinity marker will be buried inside the interior of the nascentprotein, the interaction between the affinity marker and the acceptormolecule will still occur as long as some affinity markers are exposedon the surface of the nascent protein. This is not normally a problembecause the affinity marker is distributed over several locations in theprotein sequence.

Affinity markers include native amino acids, non-native amino acids,amino acid derivatives or amino acid analogs in which a coupling agentis attached or incorporated. Attachment of the coupling agent to, forexample, a non-native amino acid may occur through covalentinteractions, although non-covalent interactions such as hydrophilic orhydrophobic interactions, hydrogen bonds, electrostatic interactions ora combination of these forces are also possible. Examples of usefulcoupling agents include molecules such as haptens, immunogenicmolecules, biotin and biotin derivatives, and fragments and combinationsof these molecules. Coupling agents enable the selective binding orattachment of newly formed nascent proteins to facilitate theirdetection or isolation. Coupling agents may contain antigenic sites fora specific antibody, or comprise molecules such as biotin which is knownto have strong binding to acceptor groups such as streptavidin. Forexample, biotin may be covalently linked to an amino acid which isincorporated into a protein chain. The presence of the biotin willselectively bind only nascent proteins which incorporated such markersto avidin molecules coated onto a surface. Suitable surfaces includeresins for chromatographic separation, plastics such as tissue culturesurfaces for binding plates, microtiter dishes and beads, ceramics andglasses, particles including magnetic particles, polymers and othermatrices. The treated surface is washed with, for example, phosphatebuffered saline (PBS), to remove non-nascent proteins and othertranslation reagents and the nascent proteins isolated. In some casethese materials may be part of biomolecular sensing devices such asoptical fibers, chemfets, and plasmon detectors.

One example of an affinity marker is dansyllysine (FIG. 5). Antibodieswhich interact with the dansyl ring are commercially available (SigmaChemical; St. Louis, Mo.) or can be prepared using known protocols suchas described in Antibodies: A Laboratory Manual (E. Harlow and D. Lane,editors, Cold Spring Harbor Laboratory Press, 1988) which is herebyspecifically incorporated by reference. Many conventional techniquesexist which would enable proteins containing the dansyl moiety to beseparated from other proteins on the basis of a specific antibody-dansylinteraction. For example, the antibody could be immobilized onto thepacking material of a chromatographic column. This method, known asaffinity column chromatography, accomplishes protein separation bycausing the target protein to be retained on the column due to itsinteraction with the immobilized antibody, while other proteins passthrough the column. The target protein is then released by disruptingthe antibody-antigen interaction. Specific chromatographic columnmaterials such as ion-exchange or affinity Sepharose, Sephacryl,Sephadex and other chromatography resins are commercially available(Sigma Chemical; St. Louis, Mo.; Pharmacia Biotech; Piscataway, N.J.).

Separation can also be performed through an antibody-dansyl interactionusing other biochemical separation methods such as immunoprecipitationand immobilization of the antibodies on filters or other surfaces suchas beads, plates or resins. For example, protein could be isolated bycoating magnetic beads with a protein-specific antibody. Beads areseparated from the extract using magnetic fields. A specific advantageof using dansyllysine as an affinity marker is that once a protein isseparated it can also be conveniently detected because of itsfluorescent properties.

In addition to antibodies, other biological molecules exist whichexhibit equally strong interaction with target molecules or chemicalmoieties. An example is the interaction of biotin and avidin. In thiscase, an affinity analog which contains the biotin moiety would beincorporated into the protein using the methods which are part of thepresent invention. Biotin-lysine amino acid analogs are commerciallyavailable (Molecular Probes; Eugene, Oreg.).

Affinity markers also comprise one component of a multicomponent complexwhich must be formed prior to detection of the marker. One particularembodiment of this detection means involves the use of luminescent metalchelates, in particular luminescent rare earth metal chelates. It iswell known that certain molecules form very stable complexes with rareearth metals. It is also well known that introduction of chromophoreinto these chelates sensitizes luminescence of these complexes. Avariety of detection schemes based on the use of luminescent rare earthmetal chelates have been described: Hemmila, I. A., “Applications ofFluorescence in Immunoassays”, (Wiley&Sons 1991).

In a preferred embodiment, tRNA is misaminoacylated with a chromophorethat also acts as a rare earth shelter. This modified aminoacyl tRNA isthen introduced into cellular or cell-free protein translation systemand the modified amino acid incorporated into nascent protein. Themixture is then separated using gel electrophoresis and the gel isincubated with a solution containing rare earth cation. Under theseconditions rare earth cations form luminescent complexes with aminoacids modified with a chelator present only in nascent proteins. Thenascent proteins are then detected using a mid-range UV transilluminator(350 nm), which excites the formed lanthanide complex. The image is thenrecorded using polaroid camera or CCD array and a filter. In oneembodiment, the derivatives of salicylic acid as one component andterbium ions as a second component of the binary detection system areused.

Affinity markers can also comprise cleavable markers incorporating acoupling agent. This property is important in cases where removal of thecoupled agent is required to preserve the native structure and functionof the protein and to release nascent protein from acceptor groups. Insome cases, cleavage and removal of the coupling agent results inproduction of a native amino acid. One such example is photocleavablebiotin coupled to an amino acid.

Photocleavable biotin contains a photoreactive moiety which comprises aphenyl ring derivatized with functionalities represented in FIG. 12 byX, Y and Z. X allows linkage of PCB to the bimolecular substrate throughthe reactive group X′. Examples of X′ include Cl,O—N-hydroxysuccinimidyl, OCH₂CN, OPhF₅, OPhCl₅, N₃. Y represents asubstitution pattern of a phenyl ring containing one or moresubstitutions such as nitro or alkoxyl. The functionality Z represents agroup that allows linkage of the cross-linker moiety to thephotoreactive moiety. The photoreactive moiety has the property thatupon illumination, it undergoes a photoreaction that results in cleavageof the PCB molecule from the substrate.

A lysine-tRNA is misaminoacylated with photocleavable biotin-lysine, orchemically modified to attach a photocleavable biotin amino acid. Themisaminoacylated tRNA is introduced into a cell-free proteinsynthesizing system and nascent proteins produced. The nascent proteinscan be separated from other components of the system bystreptavidin-coated magnetic beads using conventional methods which relyon the interaction of beads with a magnetic field. Nascent proteins arereleased then from beads by irradiation with UV light of approximately280 nm wavelength.

Many devices designed to detect proteins are based on the interaction ofa target protein with specific immobilized acceptor molecule. Suchdevices can also be used to detect nascent proteins once they containaffinity markers such as biodetectors based on sensing changes insurface plasmons, light scattering and electronic properties ofmaterials that are altered due to the interaction of the target moleculewith the immobilized acceptor group.

Nascent proteins, including those which do not contain affinity-typemarkers, may be isolated by more conventional isolation techniques. Someof the more useful isolation techniques which can be applied or combinedto isolate and purify nascent proteins include chemical extraction, suchas phenol or chloroform extract, dialysis, precipitation such asammonium sulfate cuts, electrophoresis, and chromatographic techniques.Chemical isolation techniques generally do not provide specificisolation of individual proteins, but are useful for removal of bulkquantities of non-proteinaceous material. Electrophoretic separationinvolves placing the translation mixture containing nascent proteinsinto wells of a gel which may be a denaturing or non-denaturingpolyacrylamide or agarose gel. Direct or pulsed current is applied tothe gel and the various components of the system separate according tomolecular size, configuration, charge or a combination of their physicalproperties. Once distinguished on the gel, the portion containing theisolated proteins removed and the nascent proteins purified from thegel. Methods for the purification of protein from acrylamide and agarosegels are known and commercially available.

Chromatographic techniques which are useful for the isolation andpurification of proteins include gel filtration, fast-pressure orhigh-pressure liquid chromatography, reverse-phase chromatography,affinity chromatography and ion exchange chromatography. Thesetechniques are very useful for isolation and purification of proteinsspecies containing selected markers.

Another embodiment of the invention is directed to the incorporation ofnon-native amino acids or amino acid derivatives with marker or affinityproperties at the amino-terminal residue of a nascent protein (FIG. 13).This can be accomplished by using the side chain of an amino acid or byderivatizing the terminal amino group of an amino acid. In either casethe resulting molecule is termed an amino acid derivative. Theamino-terminal residue of a protein is free and its derivatization wouldnot interfere with formation of the nascent polypeptide. The non-nativeamino acid or amino acid derivative is then used to misaminoacylate aninitiator tRNA which only recognizes the first AUG codon signaling theinitiation of protein synthesis. After introduction of thismisaminoacylated initiator tRNA into a protein synthesis system, markeris incorporated only at the amino terminal of the nascent protein. Theability to incorporate at the N-terminal residue can be important asthese nascent molecules are most likely to fold into nativeconformation. This can be useful in studies where detection or isolationof functional nascent proteins is desired.

Not all markers incorporated with misaminoacylated initiator tRNAs atthe amino-terminal residue of the nascent protein show the sameacceptance by the protein translational machinery. Furthermore, therange of incorporation of different markers can be more restrictivecompared to the use of non-initiator tRNAs such as lysyl-tRNA. Althoughthe factors influencing this descrimination between markers forincorporation by a misaminoacylated initiator tRNA are not fullyelucidated, one possibility is that the initiation factor (IF2) which isused for carrying formylmethionine-tRNA^(fmet) to ribosomes plays arole. A second possibility is that the interaction between the markerstructure and the ribosomes plays a role. For example, the marker,BODIPY-FL is accepted by the protein translational machinery to agreater extent than smaller fluorescent markers such as NBD. For thisreason, BODIPY-FL is a superior marker for use in the detection ofnascent protein when incorporated through initiator tRNAs.

A marker group can also be incorporated at the N terminal by using amutant tRNA which does not recognize the normal AUG start codon. In somecases this can lead to a higher extent of specific incorporation of themarker. For example, the mutant of initiator tRNA, where the anticodonhas been changed from CAU→CUA (resulting in the change of initiatormethionine codon to amber stop codon) has shown to act as initiatorsuppressor tRNA (Varshney U, RajBhandary U L, Proc Natl Acad Sci USA1990 February; 87(4):1586-90; Initiation of protein synthesis from atermination codon). This tRNA initiates the protein synthesis of aparticular gene when the normal initiation codon, AUG is replaced by theamber codon UAG. Furthermore, initiation of protein synthesis with UAGand tRNA(fMet^(CUA)) was found to occur with glutamine and notmethionine. In order to use this tRNA to introduce a marker at the Nterminal of a nascent protein, this mutant tRNA can be enzymaticallyaminoacylated with glutamine and then modified with suitable marker.Alternatively, this tRNA could be chemically aminoacylated usingmodified amino acid (for example methionine-BODIPY). Since proteintranslation can only be initiated by this protein on messages containingUAG, all proteins will contain the marker at the N-terminal end of theprotein.

D. Mass Spectrometry

Mass spectrometry measures the mass of a molecule. The use of massspectrometry in biology is continuing to advance rapidly, findingapplications in diverse areas including the analysis of carbohydrates,proteins, nucleic acids and biomolecular complexes. For example, thedevelopment of matrix assisted laser desorption ionization (MALDI) massspectrometry (MS) has provided an important tool for the analysis ofbiomolecules, including proteins, oligonucleotides, and oligosacharrides[Karas, 1987 #6180; Hillenkamp, 1993 #61751. This technique's successderives from its ability to determine the molecular weight of largebiomolecules and non-covalent complexes (>500,000 Da) with high accuracy(0.01%) and sensitivity (subfemtomole quantities). Thus far, it has beenfound applicable in diverse areas of biology and medicine including therapid sequencing of DNA, screening for bioactive peptides and analysisof membrane proteins.

Markers incorporated by misaminoacylated tRNAs into nascent proteins,especially at a specific position such at the N-terminal can be used forthe detection of nascent proteins by mass spectrometry. Without such amarker, it can be very difficult to detect a band due to a nascentprotein synthesized in the presence of a cellular or cell-free extractdue the presence of many other molecules of similar mass in the extract.For example, in some cases less than 0.01% of the total protein mass ofthe extract may comprise the nascent protein(s). Furthermore, moleculeswith similar molecular weight as the nascent protein may be present inthe mixture. Such molecules will overlap with peaks due to the nascentprotein. This problem is particularly severe if the nascent protein is atranscription or translation factor already present in the cell-free orcellular protein synthesis. The synthesis of additional amounts of thisprotein in the protein synthesis system would be difficult to detectusing known methods in mass spectrometry since peak intensities are notcorrelated in a linear manner with protein concentration.

Detection by mass spectrometry of a nascent protein produced in atranslation system is also very difficult if the mass of the nascentprotein produced is not known. This might situation might occur forexample if the nascent protein is translated from DNA where the exactsequence is not known. One such example is the translation of DNA fromindividuals which may have specific mutations in particular genes orgene fragments. In this case, the mutation can cause a change in theprotein sequence and even result in chain truncation if the mutationresults in a stop codon. The mass of nascent proteins produced in atranslation system might also not be known if DNA is derived fromunknown sources such as as colonies of bacteria which can containdifferent members of a gene library or fragments thereof.

In one embodiment of the invention, the incorporation of markers of aspecific mass (mass markers) into nascent proteins can be used toeliminate all of the above mentioned problems associated with theconventional mass spectrometric approach. First, a tRNA misaminoacylatedwith a marker of a known mass is added to the protein synthesis system.The synthesis system is then incubated to produce the nascent proteins.The mass spectrum of the protein synthesis system is then measured. Thepresence of the nascent protein can be directly detected by identifyingpeaks in the mass spectrum of the protein synthesis system whichcorrespond to the mass of the unmodified protein and a second band at ahigher mass which corresponds to the mass of the nascent protein plusthe modified amino acid containing the mass of the marker.

There are several steps that can be taken to optimize the efficientdetection of nascent proteins using this method. The mass of the markershould exceed the resolution of the mass spectrometer, so that theincreased in mass of the nascent protein can be resolved from theunmodified mass. For example, a marker with a mass exceeding 100 daltonscan be readily detected in proteins with total mass up to 100,000 usingboth matrix assisted laser desorption (MALDI) or electrospray ionization(ESI) techniques. The amount of misaminoacylated tRNA should be adjustedso that the incorporation of the mass marker occurs in approximately 50%of the total nascent protein produced. An initiator tRNA is preferablefor incorporation of the mass marker since it will only be incorporatedat the N-terminal of the nascent protein, thus avoiding the possibilitythat the nascent protein will contain multiple copies of the massmarker.

One example of this method is the incorporation of the marker BODIPY-FL,which has a mass of 282, into a nascent protein using a misaminoacylatedinitiator tRNA. Incorporation of this marker into a nascent proteinusing a misaminoacylated initiator tRNA causes a band to appear atapproximately 282 daltons above the normal band which appears for thenascent protein. Since the incorporation of the marker is less than oneper protein due to competition of non-misaminoacylated E.colitRNA^(fmet), a peak corresponding to the unmodified protein alsoappears. Identification of these two bands separated by the mass of themarker allows initial identification of the band due to the nascentprotein. Further verification of the band due to the nascent protein canbe made by adjusting the level of the misaminoacylated initiator tRNA inthe translation mixture. For example, if the misaminoacylated initiatortRNA is left out, than only a peak corresponding to the unmodifiedprotein appears in the mass spectrum of the protein synthesis system. Bycomparing the mass spectrum from the protein synthesis system containingand not containing the misaminacylated tRNA with the BODIPY-FL, thepresence of the nascent protein can be uniquely identified, even when aprotein with similar or identical mass is already present in the proteinsynthesis system.

For the purpose of mass spectrometric identification of nascentproteins, it is sometimes advantageous to utilize a photocleavablemarker. In this case, peaks due to nascent proteins in the mass spectrumcan be easily identified by measuring and comparing spectra from samplesof the protein synthesis system that have been exposed and not exposedto irradiation which photocleaves the marker. Those samples which arenot exposed to irradiation will exhibit bands corresponding the mass ofthe nascent protein which has the incorporated mass marker, whereasthose samples which are exposed to irradiation will exhibit bandscorresponding to the mass of the nascent proteins after removal of themass marker. This shift of specific bands in the mass spectrum due toirradiation provides a unique identifier of bands which are due to thenascent proteins in the protein synthesis system.

One example of this method involves the use of the photocleavablemarker, photocleavable biotin. When photocleavable biotin isincorporated into the test protein α-hemolysin, a toxin produced bystaphyloccus, by using the misaminoacylated E. coli initiatortRNA^(met), the mass spectrum exhibits two peaks corresponding to themass of the nascent protein 35,904 Da, and a second peak at 36,465 Dacorresponding to the mass of the nascent protein plus the mass ofphotocleavable biotin. After photocleavage of the marker by exposing thecell-free or cellular extract to UV light with a wavelength ofapproximately 365 nm for approximately 10 minutes, the two bands undergochanges in intensity due to cleavage of the marker from the nascentprotein. For example, in the case of a form of photocleavable biotincontaining a single spacer the change in the mass will be 561.57. Thesecharacteristic changes are then used to uniquely identify the peakscorresponding the nascent protein. In the case of MALDI massspectrometry, the probe laser pulses when adjusted to sufficientintensity can be used to accomplish photocleavage of photocleavablebiotin. In this case, changes can be conveniently measured during thecourse of the measurements, thereby facilitating detection of peaksassociated with the nascent protein. A similar approach can also be usedto identify more than one nascent protein of unknown mass in a cell orcell-free translation system.

Markers with affinity properties which are incorporated bymisaminoacylated tRNAs into nascent proteins can also be very useful forthe detection of such proteins by mass spectrometry. Such markers can beused to isolate nascent proteins from the rest of the cell-free orcellular translation system. In this case, the isolation of the nascentproteins from the rest of the cell-free mixture removes interferencefrom bands due to other molecules in the protein translation system. Anexample of this approach is the incorporation of photocleavable biotininto the N-terminal end of a nascent proteins using misaminoacylatedtRNA. When this marker is incorporated onto the N-terminal end of anascent protein using an E. coli tRNA^(met), it provides a convenientaffinity label which can be bound using streptavidin affinity media suchas streptavidin agarose. Once the nascent protein is separated by thismethod from the rest of the protein synthesis system, it can be releasedby UV-light and analyzed by mass spectrometry. In the case of MALDI massspectrometry, release of the nascent protein can most conveniently beaccomplished by using the UV-laser excitation pulses of the MALDIsystem. Alternatively, the sample can be irradiated prior to massspectrometric analysis in the case of MALDI or ESI mass spectrometry.

E. Electrophoresis

Another embodiment of the invention is directed to methods for detectingby electrophoresis the interaction of molecules or agents with nascentproteins which are translated in a translation system. This methodallows a large number of compounds or agents to be rapidly screened forpossible interaction with the expressed protein of specific genes, evenwhen the protein has not been isolated or its function identified. Italso allows a library of proteins expressed by a pool of genes to berapidly screened for interaction with compounds or agents without thenecessity of isolating these proteins or agents. The agents might bepart of a combinatorial library of compounds or present in a complexbiological mixture such as a natural sample. The agents might interactwith the nascent proteins by binding to them or to cause a change in thestructure of the nascent protein by chemical or enzymatic modification.

In addition to gel electrophoresis, which measures the electrophoreticmobility of proteins in gels such as polyacyralimide gel, this methodcan be performed using capillary electrophoresis. CE measures theelectrophoretic migration time of a protein which is proportional to thecharge-to-mass ratio of the molecule. One form of CE, sometimes termedaffinity capillary electrophoresis, has been found to be highlysensitive to interaction of proteins with other molecules includingsmall ligands as long as the binding produces a change in thecharge-to-mass ratio of the protein after the binding event. The highestsensitivity can be obtained if the protein is conjugated to a markerwith a specifically detectable electromagnetic spectral property such asa fluorescent dye. Detection of a peak in the electrophoresischromatogram is accomplished by laser induced emission of mainly visiblewavelengths. Examples of fluorescent dyes include fluoroscein,rhodamine, Texas Red and BODIPY.

It is very difficult to detect a nascent protein synthesized in acellular or cell-free extract by CE without subsequent isolation andlabeling steps due the need for high sensitivity detection and thepresence of many other molecules of similar mass/charge ratio in theextract. For example, in typical cases less than 0.01% of the totalprotein mass of the extract may comprise the nascent protein(s). Othermolecules with similar electrophoretic migration times as the nascentprotein may be present in the mixture. Such molecules will overlap withpeaks due to the nascent protein.

It is also very difficult using conventional methods of CE to detect theinteraction of molecules with nascent proteins produced in a cell freeor cellular synthesis system. Affinity capillary electrophoresis hasbeen found to be sensitive to interaction of proteins with othermolecules including small ligands as long as the binding produces achange in the charge-to-mass ratio of the protein after the bindingevent. However, the selective addition of a marker such as a fluorescentdye to a nascent protein is not possible using conventional meansbecause most markers reagents will nonspecifically label other moleculesin the protein synthesis system besides the nascent proteins. In somecases, it may be possible utilize a specific substrate or ligand whichbinds only to the nascent protein. However this approach requires adetailed knowledge of the binding properties of the nascent protein andspecial design of a ligand with marker properties. The nascent proteinmay also be isolated from the protein synthesis system and thenselectively labeled with a detectable marker. However, this alsorequires the development of a procedure for isolation of the nascentprotein which can be time consuming and requires extensive knowledge ofproperties of the protein or protein engineering to incorporate anaffinity epitope. Even after a nascent protein has been isolated, it isoften difficult to uniformly label the protein with a marker so that thecharge/mass ratio of each labeled protein remains the same. In the mostadvantageous form of labeling, a highly fluorescent marker isincorporated at only one specific position in the protein thus avoidinga set of proteins with different electrophoretic mobilities.

The method of the invention also overcomes major problems associatedwith the rapid screening of samples for new therapeutic compounds usingcapillary electrophoresis (CE) such as described in U.S. Pat. No.5,783,397 (hereby incorporated by reference) when the target protein isa nascent protein expressed in a translation system. This includes theneed to uniformly label expressed target proteins in a translationsystem with markers for high sensitivity analysis by CE which normallyrequires lengthy isolation steps and special techniques for uniformlabeling.

The method can also be used in conjunction with expression cloningmethod for isolating novel cDNA clones such as described in U.S. Pat.No. 565,451, which is specifically incorporated by reference. Thispatent describes novel methods to identify cDNA clones by a) collectingpools of about 100 individual bacterial colonies; and b) expressingproteins encoded by the cDNAs in the pools in vitro. Proteins which canbe identified in this manner include but are not limited to nucleic acidbinding protein, cytoskeletal protein, growth factor, differentiationfactor, post-translationally modified protein, phosphorylated protein,proteolytically cleaved protein, glycosylated protein, subunit or amultiple component of a protein complex, enzyme, isoform of a knownprotein, mutant form of known protein. Importantly, the method includesas a crucial step identifying a desired protein from protein translationsystem. Two such methods described for identifying the protein involveradioactive labeling and chemical labeling. However, these steps can beextremely time-consuming and are not conducive to rapidly screening anextract for the desired protein.

The present invention avoids all of the problems discussed above. In oneembodiment of the invention a tRNA misaminoacylated with a detectablemarker is added to the protein synthesis system. The system is incubatedto incorporate the detectable marker into the nascent proteins. One ormore molecules (agents) are then combined with the nascent proteins(either before or after isolation) to allow agents to interact withnascent proteins. Aliquots of the mixture are then subjected toelectrophoresis. Nascent proteins which have interacted with the agentsare identified by detecting changes in the electrophoretic mobility ofnascent proteins with incorporated markers. In the case where the agentshave interacted with the nascent proteins, the proteins can be isolatedand subsequently subjected to further analysis. In cases where theagents have bound to the nascent proteins, the bound agents can beidentified by isolating the nascent proteins.

In one example of this method, the fluorescent marker BODIPY-FL is usedto misaminoacylate an E. coli initiator tRNA^(fmet) as previouslydescribed. The misaminoacylated tRNA is then added to a proteinsynthesis system and the system incubated to produce nascent proteincontaining the BODIPY-FL at the N-terminal. A specific compound whichmay bind to the nascent protein is then added to the protein synthesissystem at a specific concentration. An aliquot from the mixture is theninjected into an apparatus for capillary electrophoresis. Nascentproteins in the mixture are identified by detection of the fluorescencefrom the BODIPY-FL using exciting light from an Argon laser tuned to 488run. Interaction of the specific compound is determined by comparing theelectrophoretic mobility measured of the nascent protein exposed to thespecific compound with a similar measurement of the nascent protein thathas not been exposed. The binding strength of the compound can then beascertained by altering the concentration of the specific compoundsadded to the protein synthesis system and measuring the change in therelative intensity of bands assigned to the uncomplexed and complexednascent protein.

The method is not limited to studying the interaction of one agent withone nascent protein translated in a protein translation system. Forexample, a library of compounds can be screened to identify those whichserve are ligands for specific target protein. In addition tointeractions which involve the binding of one or more agents to thenascent proteins interactions which result in a modification of thenascent protein including but not limited to phosphorylation,proteolysis, glycosylation, formation of a complex with other biologicalmolecules can be detected using the marker incorporated in the nascentproteins when combined with electrophoresis. For example, theinteraction of an antibody with the nascent proteins can be detected dueto a change in the effective electrophoretic mobility of the complexformed. A similar approach could be used to identify the presence of oneor more compounds in a complex mixture which bind to the nascentprotein. Such a mixture might constitute a library of compounds producedby combinatorial chemistry or compounds which might be present in acomplex biological mixture such as natural samples which may containtherapeutic compounds.

F. Microscale Methods

While the present invention contemplates capillary electrophoresis (seeabove), other methods are also contemplated. In particular, microscalemethods can be employed in conjunction with the novel markers (e.g.BODIPY) and methods of the present invention. The methods are“microscale” in that the dimensions of the channels on the device (andthe corresponding fluid volumes) are very small (typically in thepicometer range). For example, channels are typically betweenapproximately 0.10 and 0.50 μm in depth and between approximately 5 and500 μm in width.

Although there are many formats, materials, and size scales forconstructing integrated fluidic systems, the present inventioncontemplates microfabricated devices as a solution to the manyinefficiencies of larger scale screening. Devices can be microfabricatedfrom a number of materials. Silicon is the material used for theconstruction of computing microprocessors and its fabricationtechnologies have developed at an unprecedented pace over the past 30years. The principal modern method for fabricating semiconductorintegrated circuits is the so-called planar process. The planar processrelies on the unique characteristics of silicon and comprises a complexsequence of manufacturing steps involving deposition, oxidation,photolithography, diffusion and/or ion implantation, and metallization,to fabricate a “layered” integrated circuit device in a siliconsubstrate. See e.g., W. Miller, U.S. Pat. No. 5,091,328, herebyincorporated by reference. While this technology was initially appliedto making microelectronic devices, the same techniques are currentlybeing used for micromechanical systems.

Continuous flow liquid transport has been described using a microfluidicdevice developed with silicon. See J. Pfahler et al., Sensors andActuators, A21-A23 (1990), pp. 431-434. Pumps have also been described,using external forces to create flow, based on micromachining ofsilicon. See H. T. G. Van Lintel et al., Sensors and Actuators15:153-167 (1988). SDS capillary gel electrophoresis of proteins inmicrofabricated channels has also been described. See Yao S et al., “SDScapillary gel electrophoresis of proteins in microfabricated channels,”PNAS 96:5372 (1999). Compared to more conventional two-dimensionaldenaturing gel electorphoresis (which is generally time consuming andrequires considerable amounts of sample), this microchannel-basedseparation technique was shown to be quick and offer high resolution.

As a mechanical building material, silicon has well-known fabricationcharacteristics. The economic attraction of silicon devices is thattheir associated micromachining technologies are, essentially,photographic reproduction techniques. In these processes, transparenttemplates or masks containing opaque designs are used to photodefineobjects on the surface of the silicon substrate. The patterns on thetemplates are generated with computer-aided design programs and candelineate structures with line-widths of less than one micron. Once atemplate is generated, it can be used almost indefinitely to produceidentical replicate structures. Consequently, even extremely complexmicromachines can be reproduced in mass quantities and at lowincremental unit cost—provided that all of the components are compatiblewith the silicon micromachining process. While the present inventioncontemplates other substrates, such as glass or quartz, for use inphotolithographic methods to construct microfabricated analysis devices,silicon is preferred because of the added advantage of allowing a largevariety of electronic components to be fabricated within the samestructure.

In one embodiment, the present invention contemplates siliconmicromachined components in an integrated analysis system. Sample (e.g.a test compound) and one or more reagents (e.g. a BODIPY labellednascent protein) are injected either continuously or in pulses into thedevice through entry ports and they are transported through channels toa reaction chamber, such as a thermally controlled reactor where mixingand reactions take place. The biochemical products can be then moveddown a new channel (or by an electrophoresis module, if desired) wheremigration data is collected by a detector and transmitted to a recordinginstrument. If desired, a polymer can be used in the channels to provideresolution by molecular sieving. The biochemical products can beisolated by diverting the flow to an external port for subsequentadditional analysis. Importantly, the fluidic and electronic componentsare designed to be fully compatible in function and construction withthe biological reactions and reagents. In this embodiment, potentialtest compounds can be rapidly screened for interaction with a labelednascent protein or multiple nascent proteins that are co-expressed in atranslation reaction system. In this manner the system can be used toscreen for interaction so as to identify useful drugs.

In another embodiment, one or more components of the protein synthesissystem are introduced into the device through entry ports and they aretransported through channels to a reaction chamber, such as a thermallycontrolled reactor, where the expression of the nascent protein whichcontains the marker such as BODIPY occurs. The labeled nascent proteincan than be mixed with one or more reagents (e.g. a test compound) thatare introduced into the device through entry ports. After the reactiontakes placed, the biochemical products can be then moved down a newchannel (or by an electrophoresis module, if desired) where migrationdata is collected by a detector and transmitted to a recordinginstrument. It is to be understood that components of the proteinsynthesis system which can be introduced into the device can includemisaminoacylated tRNAs, DNA, mRNA, amino acids and nucleotides. Thecomponents can be introduced either continuously or in discrete pulses.The DNA may also be produced within the micromachined device byenzymatic reactions such as the polymerase chain reaction as has beendescribed. See Kopp et al., “Chemical Amplification: Continuous Flow PCRon a Chip,” Science 280:1046 (1998).

In silicon micromachining, a simple technique to form closed channelsinvolves etching an open trough on the surface of a substrate and thenbonding a second, unetched substrate over the open channel. There are awide variety of isotropic and anisotropic etch reagents, either liquidor gaseous, that can produce channels with well-defined side walls anduniform etch depths. Since the paths of the channels are defined by thephoto-process mask, the complexity of channel patterns on the device isvirtually unlimited. Controlled etching can also produce sample entryholes that pass completely through the substrate, resulting in entryports on the outside surface of the device connected to channelstructures.

G. Multiple Misaminoacylated tRNAs

It may often be advantageous to incorporate more than one marker into asingle species of protein. This can be accomplished by using a singletRNA species such as a lysine tRNA misaminoacylated with both a markersuch as dansyllysine and a coupling agent such as biotin-lysine.Alternatively, different tRNAs which are each misaminoacylated withdifferent markers can also be utilized. For example, the coumarinderivative could be used to misaminoacylate a tryptophan tRNA and adansyl-lysine used to misaminoacylate a lysine tRNA.

One use of multiple misaminoacylated tRNAs is to study the expression ofproteins under the control of different genetic elements such asrepressors or activators, or promoters or operators. For example, thesynthesis of proteins at two different times in response to an internalor external agent could be distinguished by introducing misaminoacylatedtRNAs at different times into the cellular or cell-free proteinsynthesis system. A tRNA^(tyr) might be charged with marker A and atRNA^(lys) charged with marker B, yielding A-tRNA^(tyr) andB-tRNA^(lys), respectively. In this case, protein one under the controlof one promoter can be labeled by adding the A-tRNA^(tyr) to thereaction system. If a second misaminoacylated tRNA, B-tRNA^(lys) is thenadded and a second promoter for protein two activated, the nascentprotein produced will contain both label A and B. Additional markerscould also be added using additional tRNA molecules to further study theexpression of additional proteins. The detection and analysis ofmultiply labeled nascent proteins can be facilitated by using themulti-colored electrophoresis pattern reading system, described in U.S.Pat. No. 5,190,632, which is specifically incorporated by reference, orother multi-label reading systems such as those described in U.S. Pat.Nos. 5,069,769 and 5,137,609, which are both hereby specificallyincorporated by reference.

A second use of multiple misaminoacylated tRNAs is in the combinedisolation and detection of nascent proteins. For example, biotin-lysinemarker could be used to misaminoacylate one tRNA and a coumarin markerused to misaminoacylate a different tRNA. Magnetic particles coated withstreptavidin which binds the incorporated lysine-biotin would be used toisolate nascent proteins from the reaction mixture and the coumarinmarker used for detection and quantitation.

A schematic diagram of the basics of the above methods is shown in FIG.14. In a first step, the marker selected (M), which may have reporter(R) or affinity (A) properties, is chemically or enzymaticallymisaminoacylated to a single tRNA species or a mixture of differenttRNAs. Prior to protein synthesis, a predetermined amount of themisaminoacylated tRNA, charged with the fluorescent marker is mixed withthe cell-free protein synthesis reaction system at concentrationssufficient to allow the misaminoacylated tRNA to compete effectivelywith the corresponding tRNA. After an incubation of about 1-3 hours, thereaction mixture is analyzed using conventional polyacrylamide oragarose gel electrophoresis. After electrophoresis, the gel isilluminated by UV radiation. Bands due to the nascent protein exhibitdistinct fluorescence and can be easily and rapidly distinguished,either visually or photographically, from non-fluorescent bands ofpreexisting proteins. Nascent proteins can be isolated by excising thefluorescent band and electroeluting the protein from the extracted gelpieces. The quantities and molecular weights of the nascent proteins canbe determined by comparison of its fluorescence with the fluorescenceproduced by a set of proteins with known molecular weights and knownquantities. The results of the assay can be recorded and stored forfurther analysis using standard electronic imaging and photographic orspectroscopic methods.

H. Resulting Compositions

Another embodiment of the invention is directed to a compositioncomprising nascent proteins isolated or purified by conventional methodsafter translation in the presence of markers. Compositions can beutilized in manufacturing for the preparation of reagents such ascoatings for tissue culture products and in the pharmaceutical industry.

Incorporation of markers into nascent proteins utilized in manufacturingfacilitates analysis of the final manufactured product or process bydetection of marker. For example, nascent proteins produced may be usedas coatings for tissue culture products. The reproducibility of aparticular coating process could be accurately determined by detectingvariations of marker emissions over the surface of the coated product.In addition, non-toxic markers incorporated into proteins encompassedwithin a pharmaceutical preparation such as a hormone, steroid, immuneproduct or cytokine can be utilized to facilitate safe and economicalisolation of that protein preparation. Such products could be useddirectly without the need for removal of marker. When very lowconcentrations of marker are preferred, limiting amounts of markedproteins could be used to follow a protein through a purificationprocedure. Such proteins can be efficiently purified and the purity ofthe resulting composition accurately determined. In addition, thepresence of markers may facilitate study and analysis of pharmaceuticalcompositions in testing. For example, markers can be utilized todetermine serum half-life, optimum serum levels and the presence orabsence of break-down products of the composition in a patient.

Alternatively, nascent proteins may contain specific markers which serveas therapeutically useful compounds such as toxic substances. Theseproteins are administered to a patient and the therapeutic moietyreleased after proteins have identified and possibly bound to theirrespective targets. Release may be electrical stimulation, photochemicalcleavage or other means whereby the moiety is specifically deposited inthe area targeted by the nascent proteins. In addition, moieties such asmodified toxins may be utilized which become toxic only after releasefrom nascent proteins. Nascent protein may also serve as apharmaceutical carrier which bestows the incorporated marker with activetherapeutic function or prevents marker from breaking down in the bodyprior to its therapeutic or imaging action.

The incorporation of cleavable markers in nascent proteins furtherprovides a means for removal of the non-native portion of the marker tofacilitate isolation of the protein in a completely native form. Forexample, a cleavable affinity marker such as photocleavable biotinintroduced into a nascent protein facilitates economical isolation ofthe protein and allows for the removal of the marker for further use asa pharmaceutical composition.

Pharmaceutical compositions of proteins prepared by translation in thepresence of markers may further comprise a pharmaceutically acceptablecarrier such as, for example, water, oils, lipids, polysaccharides,glycerols, collagens or combinations of these carriers. Usefulimmunological compositions include immunologically active compositions,such as a vaccine, and pharmaceutically active compositions, such as atherapeutic or prophylactic drug which can be used for the treatment ofa disease or disorder in a human.

I. Kits

Another embodiment of the invention is directed to diagnostic kits oraids containing, preferably, a cell-free translation containing specificmisaminoacylated tRNAs which incorporate markers into nascent proteinscoded for by mRNA or genes, requiring coupled transcription-translationsystems, and are only detectably present in diseased biological samples.Such kits may be useful as a rapid means to screen humans or otheranimals for the presence of certain diseases or disorders. Diseaseswhich may be detected include infections, neoplasias and geneticdisorders. Biological samples most easily tested include samples ofblood, serum, tissue, urine or stool, prenatal samples, fetal cells,nasal cells or spinal fluid. In one example, misaminoacylate fmet-tRNAscould be used as a means to detect the presence of bacteria inbiological samples containing prokaryotic cells. Kits would containtranslation reagents necessary to synthesize protein plus tRNA moleculescharged with detectable non-radioactive markers. The addition of abiological sample containing the bacteria-specific genes would supplythe nucleic acid needed for translation. Bacteria from these sampleswould be selectively lysed using a bacteria directed toxin such asColicin E1 or some other bacteria-specific permeabilizing agent.Specific genes from bacterial DNA could also be amplified using specificoligonucleotide primers in conjunction with polymerase chain reaction(PCR), as described in U.S. Pat. No. 4,683,195, which is herebyspecifically incorporated by reference. Nascent proteins containingmarker would necessarily have been produced from bacteria. Utilizingadditional markers or additional types of detection kits, the specificbacterial infection may be identified.

The present invention also contemplates kits which permit the GFTTdescribed above. For example, the present invention contemplates kits todetect specific diseases such as familial adenomatous polyposis. Inabout 30 to 60% of cases of familial adenomatous polyposis, the diseasedtissues also contain chain terminated or truncated transcripts of theAPC gene (S. M. Powell et al., N. Engl. J. Med. 329:1982-87, 1993).Chain termination occurs when frameshift cause a stop codon such as UAG,UAA or UGA to appear in the reading frame which terminates translation.Using misaminoacylated tRNAs which code for suppressor tRNAs, suchtranscripts can be rapidly and directly detected in inexpensive kits.These kits would contain a translation system, charged suppressor tRNAscontaining detectable markers, for example photocleavablecoumarin-biotin, and appropriate buffers and reagents. Such a kit mightalso contain primers or “pre-primers,” the former comprising a promoter,RBS, start codon, a region coding an affinity tag and a regioncomplementary to the template, the latter comprising a promoter, RBS,start codon, and region coding an affinity tag—but lacking a regioncomplementary to the template. The pre-primer permits ligation of theregion complementary to the template (allowing for customization for thespecific template used). A biological sample, such as diseased cells,tissue or isolated DNA or mRNA or PCR products of the DNA, is added tothe system, the system is incubated and the products analyzed. Analysisand, if desired, isolation is facilitated by a marker such as coumarinor biotin which can be specifically detected by its fluoresence usingstreptavidin coupled to HRP. Such kits provide a rapid, sensitive andselective non-radioactive diagnostic assay for the presence or absenceof the disease.

Experimental

The following examples illustrate embodiments of the invention, butshould not be viewed as limiting the scope of the invention. In some ofthe examples below, particular reagents and methods were employed asfollows:

-   Reagents: tRNA^(fmet), aminoacyl-tRNA synthetase, amino acids,    buffer salts, and RNase free water were purchased from Sigma (St.    Louis, Mo.). Many of the fluorescent dyes were obtained from    Molecular Probes (Eugene, Oreg,). The translation supplies including    routine kits were purchased from Promega (Madison, Wis.). Sephadex    G-25 was from Amersham-Pharmacia Biotech (Piscataway, N.J.). The in    vitro translation kits and plasmid DNAs coding for CAT (PinPoint™)    and Luciferase (pBESTluc™) were from Promega (Wisconsin-Madison,    Wis.) while DHFR plasmid DNA (pQE16-DHFR) was obtained from Qiagen    (Valencia, Calif.). The plasmid DNA for α-hemolysin, pT7-WT-H6-αHL    was kindly supplied by Prof: Hagan Bayley (Texas A &M University)    and large scale preparation of α-HL, DNA was carried out using    Qiagen plasmid isolation kit. The bacterioopsin plasmid DNA (pKKbop)    was from the laboratory stock.-   Preparation of FluoroTag tRNAs: The purified tRNA^(fmet) was first    aminoacylated with the methionine. In typical reaction, 1500    picomoles (˜1.0 OD₂₆₀) of tRNA was incubated for 45 min at 37° C. in    aminoacylation mix using excess of aminoacyl tRNA-synthetases. After    incubation, the mixture was neutralized by adding 0.1 volume of 3 M    sodium acetate, pH 5.0 and subjected to chloroform:acid phenol    extraction (1:1). Ethanol (2.5 volumes) was added to the aqueous    phase and the tRNA pellet obtained was dissolved in the water (25    μl). The coupling of NHS-derivatives of fluorescent molecules to the    α-amino group of methionine was carried out in 50 mM sodium    carbonate, pH 8.5 by incubating the aminoacylated tRNAf^(met) (25    μl) with fluorescent reagent (final concentration=2 mM) for 10 min    at 0° C. and the reaction was quenched by the addition of lysine    (final concentration=100 mM). The modified tRNA was precipitated    with ethanol and passed through Sephadex G-25 gel filtration column    (0.5×5 cm) to remove any free fluorescent reagent, if present. The    modified tRNA was stored frozen (−70° C.) in small aliquots in order    to avoid free-thaws. The modification extent of the    aminoacylated-tRNA was assessed by acid-urea gel electrophoresis.    This tRNA was found to stable at least for 6 month if stored    properly.-   Cell free synthesis of proteins and their detection: The in vitro    translation reactions were typcially carried out using E. coli T7    transcription-translation system (Promega) with optimized premix.    The typical translation reaction mixture (10 μl) contained 3 μl of    extract, 4 μl of premix, 1 μl of complete amino acid mix, 30    picomoles of fluorescent-methionyl-tRNA and 0.5 μg of appropriate    plasmid DNA. The optimized premix (1×) contains 57 mM HEPES, pH 8.2,    36 mM ammonium acetate, 210 mM potassium glutamate, 1.7 mM DTT, 4%    PEG 8000, 1.25 mM ATP, 0.8 mM GTP, 0.8 mM UTP, 0.8 mM CTP, 60 mM    phosphoenol pyruvate, 0.6 mM cAMP and 16 mM magnesium acetate. The    translation reaction was allowed to proceed for 45 min at 37° C. For    SDS-PAGE, 4-10 μl aliquot of the reaction mix was precipitated with    5-volume acetone and the precipitated proteins were collected by    centrifugation. The pellet was dissolved in 1× loading buffer and    subjected to SDS-PAGE after boiling for 5 min. SOS-PAGE was carried    out according to Laemmli and the gel was scan using Molecular    Dynamics FluorImager 595 using Argon laser as excitation source.    Alternatively, the nascent proteins in polyacrylamide gels were also    detected using an UV-transilluminator and the photographs were    carried out using Polaroid camera fitted with green filter (Tiffen    green #58, Polaroid DS34 camera filter kit).

For visualization of BODIPY-FL labeled protein, 488 nm as excitationsource was used along with a 530+/−30 narrow band excitation filter. Thegel was scanned using PMT voltage 1000 volts and either 100 or 200micron pixel size.

-   Enzyme/Protein activities: Biological activity of α-hemolysin was    carried out as follows. Briefly, various aliquots (0.5-2 μl) of in    vitro translation reaction mixture were added to 500 μl of TBSA    (Tris-buffered saline containing 1 mg/ml BSA, pH 7.5). To this, 25    μl of 10% solution of rabbit red blood cells (rRBCs) was added and    incubated at room temperature for 20 min. After incubation, the    assay mix was centrifuged for 1 min and the absorbance of    supernatant was measured at 415 nm (release of hemoglobin). The    equal amount of rRBCs incubated in 500 μl of TBSA is taken as    control while rRBCs incubated with 500 μl of water as taken 100%    lysis. The DHFR activity was measured spectrophotometrically.    Luciferase activity was determined using luciferase assay system    (Promega) and luminescence was measures using Packard Lumi-96    luminometer.-   Purification of α-HL and measurement BODIPY-FL incorporation into    α-HL: The translation of plasmid coding for α-HL (His₆) was carried    out at 100 μl scale and the α-HL produced was purified using    Talon-Sepharose (ClonTech) according manufacturer instructions. The    fluorescence incorporated into α-HL was then measured on Molecular    Dynamics FluorImager along with the several known concentration of    free BODIPY-FL (used as standard). The amount of protein in the same    sample was measured using a standard Bradford assay using Pierce    Protein Assay kit (Pierce, Rockford, Ill.).

EXAMPLE 1 Preparation of Markers

Synthesis of Coumarin Amino Acid: 4-(Bromomethyl)-7-methoxy coumarin(FIG. 15, compound 1; 6.18 mmole) and diethylacetamidomalonate (FIG. 15,compound 2; 6.18 mmole) were added to a solution of sodium ethoxide inabsolute ethanol and the mixture refluxed for 4 hours. The intermediateobtained (FIG. 15, compound 3) after neutralization of the reactionmixture and chloroform extraction was further purified bycrystallization from methanolic solution. This intermediate wasdissolved in a mixture of acetone and HCl (1:1) and refluxed for onehour. The reaction mixture was evaporated to dryness, and the amino acidhydrochloride precipitated using acetone. This hydrochloride wasconverted to free amino acid (FIG. 15, compound 4) by dissolving in 50%ethanol and adding pyridine to pH 4-5. The proton (¹H) NMR spectrum ofthe free amino acid was as follows: (m.p. 274-276° C., decomp.) —OCH₃ (δ3.85 s, 3H), —CH₂-(δ3.5 d, 2H), α-CH— (δ2.9 t, 1H), CH—CO (ε 6.25 s,1H), ring H (δ 7.05 s, 1H), (δ 7.8 d, 2H).

Synthesis of Fmoc derivative of coumarin: Coumarin amino acid (1.14mmol) was reacted with Fluorenylmethyloxycarbonyl N-hydroxysuccininmidylester (Fmoc-NHS ester) 1.08 mmol) in the presence of 1.14 mmol oftriethylamine for 30 minutes at room temperature. The reaction mixturewas acidified and the precipitate washed with 1 N HCl and dried. The NMRspectrum of the free amino acid was as follows: (MP 223-225° C.) —OCH₃(δ 3.85 s, 3H), —CH₂Br (δ 3.5 broad singlet, 2H), α-CH—(δ 3.0 t, 1H),CH—CO (δ 6.22 m, 1H), ring H (δ 7.05 s, 1H), (δ 7.8 d, 2H), fluorene HCH₂—CH (8 4.2 m, 2H), CH₂—CH (8 4.25 m, 1H), aromatic regions showedcharacteristic multiplets.

Synthesis of PCB: Photocleavable biotin was synthesized as describedbelow. 2-bromo, 2′-nitroacetophenone (FIG. 15, compound 5) was convertedfirst into its hexamethyltetraamommonium salt which was decomposed toobtain 2-amino, 2′-nitroacetophenone (FIG. 15, compound 6). BiotinN-hydroxysuccinimidyl ester (FIG. 15, compound 7; Sigma Chemical; St.Louis, Mo.) was reacted with a 6-aminocaproic acid (FIG. 15, compound 8)to obtain the corresponding acid (FIG. 15, compound 9). This acid wascoupled with the 2-amino, 2′nitroacetophenone using DCC to obtain theketone (FIG. 15, compound 10). The ketone was reduced using sodiumborohydride to obtain the alcohol (FIG. 15, compound 11) which wasfurther converted into its chloroformate derivative (FIG. 15, compound12). The proton NMR spectrum of the derivative (compound 12) was asfollows: (δ 1,3 m, 3H), (δ 1.4 m, 2H), (δ 1.5 m, 5H) (δ 1.62 m, 1H), (δ2.1 t, 2H) (δ 2.4 t, 2H), (δ 2.6 d, 1H), (δ 2.8 m, 1H), (δ 3.0 t, 1H),(δ 3.1 m 1H), (δ 4.15 qt, 1H) (δ 4.42 qt, 1H), (δ 5.8 t, 1H), (δ 6.25 s,1H), (δ 6.45 s, 1H), (δ 7.5 t, 1H), (δ 7.75 m, 4H), (δ 7.9 d, 1H).

EXAMPLE 2 Misaminoacylation of tRNA

The general strategy used for generating misaminoacylated tRNA is shownin FIG. 16 and involved truncation of tRNA molecules, dinucleotidesynthesis (FIG. 17), aminoacylation of the dinucleotide (FIG. 18) andligase mediated coupling.

a) Truncated tRNA molecules were generated by periodate degradation inthe presence of lysine and alkaline phosphatase basically as describedby Neu and Heppel (J. Biol. Chem. 239:2927-34, 1964). Briefly, 4 mmolesof uncharged E. coli tRNA^(Lys) molecules (Sigma Chemical; St. Louis,Mo.) were truncated with two successive treatments of 50 mM sodiummetaperiodate and 0.5 M lysine, pH 9.0, at 60° C. for 30 minutes in atotal volume of 50 μl. Reaction conditions were always above 50° C. andutilized a 10-fold excess of metaperiodate. Excess periodate wasdestroyed treatment with 5 μl of 1M glycerol. The pH of the solution wasadjusted to 8.5 by adding 15 μl of Tris-HCl to a final concentration of0.1 M. The reaction volume was increased to 150 μl by adding 100 μl ofwater. Alkaline phosphatase (15 μl, 30 units) was added and the reactionmixture incubated again at 60° C. for two hours. Incubation was followedby ethanol precipitation of total tRNA, ethanol washing, drying thepellet and dissolving the pellet in 20 μl water. This process wasrepeated twice to obtain the truncated tRNA.

b) Dinucleotide synthesis was carried out basically as performed byHudson (J. Org. Chem. 53:617-24, 1988), and can be described as a threestep process, deoxycytidine protection, adenosine protection anddinucleotide synthesis.

Deoxycytidine protection: All reaction were conducted at roomtemperature unless otherwise indicated. First, the 5′ and 3′ hydroxylgroups of deoxycytidine were protected by reacting with 4.1 equivalentsof trimethylsilyl chloride for 2 hours with constant stirring. Exocyclicamine function was protected by reacting it with 1.1 equivalents ofFmoc-Cl for 3 hours. Deprotection of the 5′ and 3′ hydroxyl wasaccomplished by the addition of 0.05 equivalents of KF and incubationfor 30 minutes. The resulting product (FIG. 17, compound 19) wasproduced at an 87% yield. Phosphate groups were added by incubating thiscompound with 1 equivalent of bis-(2-chlorophenyl)phosphorochloridateand incubating the mixture for 2 hours at 0° C. The yield in this casewas 25-30%.

Adenosine protection: Trimethylsilyl chloride (4.1 equivalents) wasadded to adenosine residue and incubated for 2 hours, after which, 1.1equivalents of Fmoc-Cl introduced and incubation continued for 3 hours.The TMS groups were deprotected with 0.5 equivalents of fluoride ions asdescribed above. The Fmoc protected adenosine (compound 22) was obtainedin a 56% yield. To further protect the 2′-hydroxyl, compound 22 wasreacted with 1.1 equivalents of tetraisopropyl disiloxyl chloride(TIPDSCl₂) for 3 hours which produces compound 23 at a 68-70% yield. Thecompound was converted to compound 24 by incubation with 20 equivalentsof dihydropyran and 0.33 equivalents of p-toluenesulfonic acid indioxane for about 4-5 hours. This compound was directly convertedwithout isolation into compound 25 (FIG. 17) by the addition of 8equivalents of tetrabutyl ammonium fluoride in a mixture oftetrahydro-furan, pyridine and water.

Dinucleotide synthesis: The protected deoxycytidine, compound 20, andthe protected adenosine, compound 25 (FIG. 17), were coupled by theaddition of 1.1 equivalents of 2-chlorophenyl bis-(1-hydroxybenzotriazolyl)phosphate in tetrahydrofuran with constant stirring for30 minutes. This was followed by the addition of 1.3 equivalents ofprotected adenosine, compound 25, in the presence of N-methylimidazolefor 30 minutes. The coupling yield was about 70% and the proton NMRspectrum of the coupled product, compound 26 (FIG. 17), was as follows:(δ 8.76 m, 2H), (δ8.0 m, 3H), (δ 7.8 m, 3H) (δ 7.6 m, 4H), (δ 7.5 m,3H), (δ 7.4 m, 18H), (δ 7.0 m, 2H), (δ 4.85 m, 14H), (δ 4.25 m, 1H); (δ3.6 m, 2H), (δ 3.2 m, 2H) (δ 2.9 m, 3H), (δ 2.6 m, 1H), (δ 2.0-1.2 m,7H).

c) Aminoacylation of the dinucleotide was accomplished by linking theprotected marker amino acid, Fmoc-coumarin, to the dinucleotide with anester linkage. First, the protected amino acid was activated with 6equivalents of benzotriazol-1-yl-oxy tris-(dimethylamino) phosphoniumhexafluoro phosphate and 60 equivalents of 1-hydroxybenzotriazole intetrahydrofuran. The mixture was incubated for 20 minutes withcontinuous stirring. This was followed with the addition of 1 equivalentof dinucleotide in 3 equivalents N-methylimidazole, and the reactioncontinued at room temperature for 2 hours. Deprotection was carried outby the addition of tetramethyl guanidine and 4-nitrobenzaldoxime, andcontinuous stirring for another 3 hours. The reaction was completed bythe addition of acetic acid and incubation, again with continuousstirring for 30 minutes at 0° C. which produced the aminoacylateddinucleotide (FIG. 18).

d) Ligation of the tRNA to the aminoacylated dinucleotide was performedbasically as described by T. G. Heckler et al. (Tetrahedron 40: 87-94,1984). Briefly, truncated tRNA molecules (8.6 O.D.₂₆₀ units/ml) andaminoacylated dinucleotides (4.6 O.D.₂₆₀ units/ml), were incubated with340 units/ml T4 RNA ligase for 16 hours at 4° C. The reaction bufferincluded 55 mM Na-Hepes, pH 7.5, 15 mM MgCl₂, 250 μM ATP, 20 μg/ml BSAand 10% DMSO. After incubation, the reaction mixture was diluted to afinal concentration of 50 mM NaOAc, pH 4.5, containing 10 mM MgCl₂. Theresulting mixture was applied to a DEAE-cellulose column (1 ml),equilibrated with 50 mM NaOAc, pH 4.5, 10 mM MgCl₂, at 4° C. The columnwas washed with 0.25 mM NaCl to remove RNA ligase and other non-tRNAcomponents. The tRNA-containing factions were pooled and loaded onto aBD-cellulose column at 4° C., that had been equilibrated with 50 mMNaOAc, pH 4.5, 10 mM MgCl₂, and 1.0 M NaCl. Unreacted tRNA was removedby washes with 10 ml of the same buffer. Pure misaminoacylated tRNA wasobtained by eluting the column with buffer containing 25% ethanol.

EXAMPLE 3 Preparation of Extract and Template

Preparation of extract: Wheat germ embryo extract was prepared byfloatation of wheat germs to enrich for embryos using a mixture ofcyclohexane and carbon tetrachloride (1:6), followed by drying overnight(about 14 hours). Floated wheat germ embryos (5 g) were ground in amortar with 5 grams of powdered glass to obtain a fine powder.Extraction medium (Buffer I: 10 mM trisacetate buffer, pH 7.6, 1 nMmagnesium acetate, 90 mM potassium acetate, and 1 mM DTT) was added tosmall portions until a smooth paste was obtained. The homogenatecontaining disrupted embryos and 25 ml of extraction medium wascentrifuged twice at 23,000×g. The extract was applied to a SephadexG-25 fine column and eluted in Buffer II (10 mM trisacetate buffer, pH7.6, 3 mM magnesium acetate, 50 mM potassium acetate, and 1 mM DTT). Abright yellow band migrating in void volume and was collected (S-23) asone ml fractions which were frozen in liquid nitrogen.

Preparation of template: Template DNA was prepared by linearizingplasmid pSP72-bop with EcoRI. Restricted linear template DNA waspurified by phenol extraction and DNA precipitation. Large scale mRNAsynthesis was carried out by in vitro transcription using theSP6-ribomax system (Promega; Madison, Wis.). Purified mRNA was denaturedat 67° C. for 10 minutes immediately prior to use.

EXAMPLE 4 Cell-Free Translation Reactions

The incorporation mixture (100 μl) contained 50 μl of S-23 extract, 5 mMmagnesium acetate, 5 mM Tris-acetate, pH 7.6, 20 mM Hepes-KOH buffer, pH7.5; 100 mM potassium acetate, 0.5 mM DTT, 0.375 mM GTP, 2.5 mM ATP, 10mM creatine phosphate, 60 μg/ml creatine kinase, and 100 μg/ml mRNAcontaining the genetic sequence which codes for bacterioopsin.Misaminoacylated PCB-lysine or coumarin amino acid-tRNA^(lys) moleculeswere added at 170 μg/ml and concentrations of magnesium ions and ATPwere optimized. The mixture was incubated at 25° C. for one hour.

EXAMPLE 5 Isolation of Nascent Proteins Containing PCB-Lysine

Streptavidin coated magnetic Dynabeads M-280 (Dynal; Oslo, Norway),having a binding capacity of 10 μg of biotinylated protein per mg ofbead. Beads at concentrations of 2 mg/ml, were washed at least 3 timesto remove stabilizing BSA. The translation mixture containing PCB-lysineincorporated into nascent protein was mixed with streptavidin coatedbeads and incubated at room temperature for 30 minutes. A magnetic fieldwas applied using a magnetic particle concentrator (MPC) (Dynal; Oslo,Norway) for 0.5-1.0 minute and the supernatant removed with pipettes.The reaction mixture was washed 3 times and the magnetic beads suspendedin 50 μl of water.

Photolysis was carried out in a quartz cuvette using a Black-Raylongwave UV lamp, Model B-100 (UV Products, Inc.; San Gabriel, Calif.).The emission peak intensity was approximately 1100 μW/cm² at 365 nm.Magnetic capture was repeated to remove the beads. Nascent proteinsobtained were quantitated and yields estimated at 70-95%.

EXAMPLE 6 The Lower Limit of Detection Using Fluorescence

Bovine serum albumin (BSA), suspended at 0.25 mg/ml in borate buffer, pH8.0, was combined with a 25 fold molar excess fluorescamine (SigmaChemical; St. Louis, Mo.) at 50 mg/ml to produce a modified, fluorescentBSA. Various amounts of modified protein (1 ng, 5 ng, 10 ng, 25 ng, 50ng, 75 ng, 100 ng, 150 ng, 200 ng) were suspended in loading buffer(bromophenol blue, glycerol, 2-mercaptoethanol, Tris-HCl, pH 6.8, SDS),and added to individual wells of a 1.5 mm thick, 12% polyacrylamide gelwith a 3% stacker. The water cooled gel was electrophoresed for 4 hoursat 50 volts. After electrophoresis, the gel was removed from theelectrophoresis apparatus, placed on a UV transilluminator andphotographed with polaroid Type 667 film using an exposure time of 10seconds. The lowest limit of detection observed under theses conditionswas 10 ng. These results indicate that using equipment found in atypical molecular biology lab, fluorescently labeled proteins can bedetected at ng quantities. Using even more sophisticated detectionprocedures and devices the level of detection can be increased evenfurther.

EXAMPLE 7 Nascent Proteins Containing Coumarin-Amino Acid

Cell-free translation is performed as described using charged tRNA^(lys)molecules misaminoacylated with lysine coupled to a benzopyrenefluorophore moiety and human 65 -interferon mRNA which contains 21codons for lysine. Samples of the mixture are supplemented with buffercontaining bromophenol blue, glycerol, 2-mercaptoethanol, Tris-HCl, pH6.8, and SDS, and directly applied to a 12% poly-acrylamide gel (3%stacker) along with a set of molecular weight markers. Electrophoresisis performed for 3 hours at 50 volts. The gel is removed from theelectrophoresis apparatus and to photographed under UV light. Bands offluorescently labeled interferon protein are specifically detected at amolecular weight of about 25 KDa. No other significant fluorescentactivity is observed on the gel. Free misaminoacylated tRNA moleculesmay be electrophoresed off of the gel and not specifically detected.

EXAMPLE 8 In Vivo Half-Life of a Pharmaceutical Composition

Cell-free translation reactions are performed by mixing 10 μl ofPCB-coumarin amino acid-tRNA^(leu), prepared by chemicalmisaminoacylation as described above and suspended in TE at 1.7 mg/ml),50 μl of S-23 extract, 10 μl water and 10 μl of a solution of 50 mMmagnesium acetate, 50 mM Tris-acetate, pH 7.6, 200 mM Hepes-KOH buffer,pH 7.5; 1 M potassium acetate, 5 mM DTT, 3.75 mM GTP, 25 mM ATP, 100 mMcreatine phosphate and 600 μg/ml creatine kinase. This mixture is kepton ice until the addition of 20 μl of 500 μg/ml human IL-2 mRNA(containing 26 leucine codons) transcribed and isolated from recombinantIL-2 cDNA. The mixture is incubated at 25° C. for one hour and placed onice. 100 μl of streptavidin coated magnetic Dynabeads (2 mg/ml) areadded to the mixture which is placed at room temperature for 30 minutes.After incubation, the mixture is centrifuged for 5 minutes in amicrofuge at 3,000×g or, a magnetic field is applied to the solutionusing a MPC. Supernatant is removed and the procedure repeated threetimes with TE. The final washed pellet is resuspended in 50 μl of 50 mMTris-HCl, pH 7.5 and transferred to a quartz cuvette. UV light from aBlack-Ray longwave UV lamp is applied to the suspension forapproximately 1 second. A magnetic field is applied to the solution witha MPC for 1.0 minute and the supernatant removed with a pipette. Thesupernatant is sterile filtered and mixed with equal volumes of sterilebuffer containing 50% glycerol, 1.8% NaCl and 25 mM sodium bicarbonate.Protein concentration is determined by measuring the O.D.₂₆₀.

0.25 ml of the resulting composition is injected i.v. into the tail veinof 2 Balb/c mice at concentrations of 1 mg/ml. Two control mice are alsoinjected with a comparable volume of buffer. At various time points (0,5 minutes, 15 minutes, 30 minutes, 60 minutes, 2 hours and 6 hours), 100μl serum samples are obtained from foot pads and added to 400 μl of 0.9%saline. Serum sample are added to a solution of dynabeads (2 mg/ml)coated with anti-coumarin antibody and incubated at room temperature for30.minutes. A magnetic field is applied to the solution with a MPC for 1minute and the supernatant removed with a pipette. Fluorescence at 470nm is measured and the samples treated with monoclonal antibody specificfor rat IL-2 protein. IL-2 protein content is quantitated for eachsample and equated with the amount of fluorescence detected. From theresults obtained, in vivo IL-2 half-life is accurately determined.

EXAMPLE 9 Incorporation of Various Fluorophores into α-Hemolysin

E. coli tRNA^(fmet) was first quantitatively aminoacylated withmethionine and the α-amino group was specifically modified usingNHS-derivatives of several fluorophores. The list of fluorescentreporter molecules (fluorophores) tested and their properties are givenin Table 2. Under the modification conditions, the modifiedMet-tRNA^(fmet) is found to be stable as assessed by acid-urea gel.Since all the fluorescent molecules tested have different opticalproperties (excitation and emission), we have determined their relativefluorescence intensity under the condition which were used for thequantitation of gels containing nascent protein.

Fluorescent detection of nascent protein was first evaluated usingα-hemolysin (α-HL) as a model protein (with C-terminal His₆-tag). α-HLis relatively small protein (32 kDa) and could be produced efficientlyin in vitro translation. In addition, its activity can be measureddirectly in the protein translation mixture using a rabbit red bloodcell hemolysis assay. In vitro translation of α-HL was carried out usingan E. coli T7 S30 transcription/translation extract (Promega Corp.,Madison, Wis.) in the presence of several different modifiedmethionyl-tRNA^(fmet) as described above. After the reaction, an aliquot(3-5 μl) was subjected to SDS-PAGE analysis and the fluorescent bandswere detected and quantitated using a FluorImager F595 (MolecularDynamics, Sunnyvale, Calif.).

The data is presented in FIG. 20. Lane 1 is a no DNA control. Lane 2shows the results with BODIPY-FL-SSE. Lane 3 shows the results withBODIPY-FL-SE. Lane 4 shows the results with NBD (see Table 2 for thestructure). Lane 5 shows the results with Bodipy-TMR. Lane 6 shows theresults with BODIPY R6G. Lanes 7, 8, 9 and 10 show the results achievedwith FAM, SFX, PYMPO and TAMRA, respectively (see Table 2 forstructures).

The results clearly indicate the α-HL produced in presence ofBODIPY-FL-methionyl-tRNA^(fmet) (lanes 2 and 3) exhibited the highestfluorescence (all the data is normalized to the BODIPY-FL-SSE. The twodifferent BODIPY-FL reagents (BODIPY-FL sulfosuccinimidyl ester (SSE)and BODIPY-FL succinimidyl ester (SE)), differ only with respect tosolubility. The next best fluorophore evaluated,6-(tetramethylrhodamine-5-(and-6)-carboxamido)hexanoic acid,succinimidyl ester (TAMRA-X, SE), exhibited 35% of the fluorescence(corrected for relative fluorescence) of BODIPY-FL-SSE. Two other formsof BODIPY, BODIPY-TMR, SE(6-((4,4-difluoro-1,3-dimethyl-5-(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene-2-propionyl)amino)hexanoicacid, succinimidyl ester) and BODIPY-R6G, SE(4,4-difluoro-5-phenyl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid,succinimidyl ester) exhibited less than 3% of the fluorescence ofBODIPY-FL, SSE . Succinimidyl6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminohexanoate (NBD-X-SE), afluorescent molecule which has previously been incorporated into theneuorkinin-2 receptor. exhibited only 6% of the BODIPY-FL-SSE. The twofluorescein analogs 5-(and-6)-carboxyfluorescein, succinimidyl-ester(FAM, SE) and 6-(fluorescein-5-(and--6) carboxamido)hexanoic acid,succinimidyl ester (SFX, SE) also showed very low fluorescence (8.4% and4.6%, respectively relative to BODIPY-FL).

EXAMPLE 10 Optimizing Incorporation

In order to optimize the amount of BODIPY-FL incorporated into nascentproteins, the translation reaction for α-HL was carried out in presenceof increasing amounts of BODIPY-FL-methionyl-tRNA^(fmet) ranging from 3-60 picomoles per reaction. All reactions yielded similar amount of α-HLas determined by hemolysis activity of rabbit red blood cells indicatingthat the exogenously added BODIPY-FL-methionyl-tRNA^(fmet) in this rangedid not inhibit protein synthesis. In contrast, the to intensity of thefluorescent band corresponding to α-HL continued to increase up to 30picomoles BODIPY-FL-methionyl-tRNA per 10 μl reaction (data not shown).Increases above this level produced no further increase in fluorescence,thus subsequent reactions were performed using this level ofBODIPY-FL-methionyl-tRNA.

A second step used to optimize BODIPY-FL incorporation was based oneliminating N-formyl-tetrahydrofolate (fTHF) from the reaction mixture.In prokaryotes, N-formyl-tetrahydrofolate (fTHF) acts as a cofactor forthe enzyme methionyl-tRNA transformylase, which formylates the initiatortRNA after its aminoacylation with methionine. Protein synthesis is theninitiated using this modified tRNA (formyl-methionine-tRNA). Withoutlimiting the invention to any particular mechanism, it is believed thateliminating fTHF from the reaction mixture reduces the competition forinitiation of protein synthesis between this endogenous initiator tRNAand exogenously added modified-initiator RNA by preventing theformylation of endogenous initiator tRNA. This was confirmed bymeasuring fluorescence directly from SDS-PAGE for reactions for whichfTHF was present and absent from the reaction mixture. In the latercase, a 2-3 fold increase in fluorescence was found (data not shown).

EXAMPLE 11 Incorporation Into Other Proteins

In order to explore the general applicability of this approach,transcription/translation reactions with BODIPY-FL-methionyl-tRNA^(fmet)were carried out using various plasmid DNAs coding for dihydrofolatereductase (DHFR), luciferase, chloramphenicol acetyl-transferase (CAT)and bacteriorhodopsin (BR). BR was included because it representsmembrane proteins; which are typically very hydrophobic. An optimizedcoupled transcription/translation system was used along with freeBODIPY-FL and BODIPY-FL-methionyl-tRNA^(fmet) using the Talon metalchelate resin (ClonTech, Palo Alto, Calif.) in order to examineincorporation into other proteins. The results are shown in FIGS. 21A(visualization using laser based Molecular Dynamics FluorImager 595) and21B (visualization using a UV-transilluminator). Lane 1 is a no DNAcontrol. Lanes 2, 3, 4, 5 and 6 are hemolysin, DHFR, Luciferase, CAT andbacteriohodopsin, respectively.

Fluorescent bands are observed using a fluorescence scanner for each ofthe proteins at positions corresponding to their relative molecular. Inthe case of luciferase, bands are observed which correspond to theexpected products of false initiation at internal methionines (PromegaTechnical Bulletin TB219). Bands corresponding to all of the proteinscould also be observed visually and recorded photographically using a UVtransilluminator (UVP TMW-20) combined with an emission filter thatallows light with λ>450 nm (FIG. 21B). Excitation in this case is likelyoccur in the UV absorbing band of BODIPY-FL which extends from 300-400nm.

The amount of BODIPY incorporation was then determined by measuring theamount of incorporated BODIPY-FL and protein present in the purifiedsample by comparison with solutions of different concentrations ofBODIPY-FL and using a Bradford protein assay, respectively. The averageof three such measurements yielded a molar ratio of 0.29+/−0.03%.However, the incorporation yield is likely to be higher sincefluorescence quenching of BODIPY-FL with protein residues such astryptophan and tyrosine may lower the fluorescence quantum yieldcompared to BODIPY-FL in aqueous solution.

The effects of the fluorescence labeling procedure on the activity ofthe nascent proteins synthesized was also evaluated. This is importantin cases where it is desirable to perform downstream functional analysissuch as in the case of in vitro expression cloning and other proteomicapplications of in vitro technology. Although it is possible for theN-terminal fluorescent label to alter the function of a protein, the lowmolar incorporation level (˜0.3%) should not significantly alter theoverall activity of the extract. This is confirmed by various enzymeassays and no significant difference is found for the activity measuredfor DHFR, α-HL and luciferase synthesized in the presence and absence ofthe BODIPY-FL-methionyl-tRNA^(fmet) (see Table 3).

EXAMPLE 12 Measuring the Sensitivity

In order to estimate the sensitivity of the method, various dilutions ofthe translation extract corresponding to 0.003-0.5 μl of the originalreaction mixture were analyzed by SDS-PAGE. As a control, extract from areaction performed without DNA was analyzed. As seen in FIG. 22B,fluorescence from α-HL bands corresponding to as small as 0.007 μl ofthe original reaction mixture were detectable. Based on the ourestimation of total nascent protein produced in the in vitro system,which ranged from 50-80 μg/ml, this corresponds to 0.35-0.5 nanograms ofα-hemolysin. This compares favorably with the sensitivity obtainableusing radioisotope labeling of nascent proteins where such a lowexpression of nascent protein may required longer exposure to X-ray filmwhich might result in serious background problem. It also exceeds thesensitivity of measuring proteins on gels currently with commerciallyavailable dyes such as coomasie blue (8-100 nanograms). Furtherimprovements in sensitivity are expected by increasing the level ofBODIPY-FL incorporation and by reducing background fluorescence, whichappears to be due to fluorescent impurities in the gel material, extractand modified tRNA added.

EXAMPLE 13 Synthesis as a Function of Time

The ability of the fluorescent labeling approach to monitor the nascentprotein synthesis as a function of time was also evaluated. For thispurpose, small aliquots of the α-HL transcription/translation mixture (4μl) were withdrawn at various times during the reaction and analyzed bySDS-PAGE. As seen in FIG. 22A, bands due to α-HL can clearly be detectedas early as 5 minutes after initiation of the incubation. Synthesis offluorescently labeled α-HL appears to saturate after 15 minutes oftranslation.

EXAMPLE 14 The Modifying Reagent

In the case of post-aminoacylation modifications used to form amisaminoacylated tRNA, an important factor is the modifying reagent usedto add the modification to the natural amino acid. For example, in thecase of the fluorophore BODIPY FL, there are two different commerciallyavailable BODIPY FL NHS reagents known as BODIPY-FL-SE and BODIPY-FL-SSE(Molecular Probes). Both reagents are based on N-hydroxysucinimide (NHS)as the leaving group. However, the two forms differ in aqueoussolubility due to the presence in one form (SSE) of a sulonate (sulfo)group (see Table 2 for structures). In this example, optimized reactionsbased on standard biochemical procedures were performed aimed at addingthe BODIPY FL fluorophore to a purified tRNA^(fmet) which isaminoacylated with methionine using these two different reagents. Forthis purpose, first the tRNA^(fmet) was aminoacylated with themethionine. In typical reaction, 1500 picomoles (˜1.0 OD₂₆₀) of tRNA wasincubated for 45 min at 37(C in aminoacylation mix using excess ofaminoacyl tRNA-synthetases. The aminoacylation mix consisted of 20 mMimidazole-HCl buffer, pH 7.5, 150 mM NaCl, 10 mM MgCl₂, 2 mM ATP and1600 units of aminoacyl tRNA-synthetase. The extent of aminoacylationwas determined by acid-urea gel as well as using ³⁵S-methionine. Afterincubation, the mixture was neutralized by adding 0.1 volume of 3 Msodium acetate, pH 5.0 and subjected to chloroform:acid phenol (pH 5.0)'extraction (1:1). Ethanol (2.5 volumes) was added to the aqueous phaseand the tRNA pellet obtained was dissolved in water (37.5 (1) and usedfor modification.

A. Modification of Aminoacylated tRNA with BODIPY-FL-SSE

To the above aminoacylated-tRNA solution, 2.5 (1 of 1N NaHCO₃ was added(final conc. 50 mM, pH=8.5) followed by 10 (1 of 10 mM solution ofBODIPY-FL-SSE (Molecular Probes) in water. The mixture was incubated for10 min at 0° C. and the reaction was quenched by the addition of lysine(final concentration=100 mM). To the resulting solution 0.1 volume of 3M NaOAc, pH=5.0 was added and the modified tRNA was precipitated with 3volumes of ethanol. Precipitate was dissolved in 50m1 microliters ofwater and purified on Sephadex G-25 gel filtration column (0.5×5 cm) toremove any free fluorescent reagent, if present. The modified tRNA wasstored frozen (−70° C.) in small aliquots in order to avoid free-thaws.

B. Modification of Aminoacylated tRNA with BODIPY-FL-SE

To the above aminoacylated-tRNA solution, 2.5 (1 of 1N NaHCO₃ (finalconc. 50 mM, pH=8.5) and 20 (1 of DMSO was added followed by 10 (1 of 10mM solution of BODIPY-FL-SE (Molecular Probes) in DMSO. The mixture wasincubated for 10 min at 0° C. and the reaction was quenched by theaddition of lysine (final concentration=100 mM). To the resultingsolution 0.1 volume of 3 M NaOAc, pH=5.0 was added and the modified tRNAwas precipitated with 3 volumes of ethanol. Precipitate was dissolved in50 ml of water and purified on Sephadex G-25 gel filtration column(0.5×5 cm) to remove any free fluorescent reagent, if present. Themodified tRNA was stored frozen (−70° C.) in small aliquots in order toavoid free-thaws.

C. Analysis

It was found empirically using HPLC that the extent of modification ofthe (alpha-amino group of methionine is substantially greater using thesulfonated form of NHS BODIPY FL compared to the non-sulfonated form ofNHS-BODIPY FL reagent. In addition the misaminoacylated tRNA^(fmet)formed using the sulfonated form was found to exhibit superiorproperties. When used in an optimized S30 E.coli translation systems toincorporate BIDOPY FL into the protein (hemolysin using a plasmidcontaining the HL gene under control of a T7 promoter), the band on anSDS-PAGE gel corresponding to the expressed HL exhibited anapproximately 2 times higher level of fluorescence when detected using aargon laser based fluoroimager compared to a similar system using themisaminoacylated formed using the non-sulfonated form.

D. Coumarin

A similar result to that described above was obtained by comparing thenon-sulfonated and sulfonated NHS derivitives of coumarin, which arealso commercially available and referred to respectively as succinimidyl7-amino-methyl-amino-coumarin acetate (AMCA-NHS; Molecular Probes) andsulfosuccinimidyl 7-amino-4-methylcoumarin-3-acetate (AMCA-sulfo-NHS;Pierce Chemicals). In this case, optimized reactions were performedusing these two different reagents based on standard biochemicalprocedures in order to add the coumarin fluorophore to a purifiedtRNA^(fmet) which is aminoacylated with methionine.

To the aminoacylated-tRNA solution described above, 2.5 (1 of 1N NaHCO₃was added (final conc. 50 mM, pH=8.5) followed by 10 (1 of 10 mMsolution of sulfosuccinimidyl 7-amino-4-methylcoumarin-3-acetate(AMCA-sulfo-NHS; Pierce Chemicals) in water. The mixture was incubatedfor 10 min at 0(C and the reaction was quenched by the addition oflysine (final concentration=100 mM). To the resulting solution 0.1volume of 3 M NaOAc, pH=5.0 was added and the modified tRNA wasprecipitated with 3 volumes of ethanol. Precipitate was dissolved in 50microliters of water and purified on Sephadex G-25 gel filtration column(0.5×5 cm) to remove any free fluorescent reagent, if present. Themodified tRNA was stored frozen (−70° C.) in small aliquots in order toavoid free-thaws.

To the above aminoacylated-tRNA solution, 2.5 (1 of 1N NaHCO₃ (finalconc. 50 mM, pH=8.5) and 20 (1 of DMSO was added followed by 10 (1 of 10mM solution of succinimidyl 7-amino-methyl-amino-coumarin acetate(AMCA-NHS; Molecular Probes) in DMSO. The mixture was incubated for 10min at 0° C. and the reaction was quenched by the addition of lysine(final concentration=100 mM). To the resulting solution 0.1 volume of 3M NaOAc, pH=5.0 was added and the modified tRNA was precipitated with 3volumes of ethanol. Precipitate was dissolved in 50 microliter of waterand purified on Sephadex G-25 gel filtration column (0.5×5 cm) to removeany free fluorescent reagent, if present. The modified tRNA was storedfrozen (−70° C.) in small aliquots in order to avoid free-thaws.

In this case, the coumarin-methionine-tRNA^(fmet) formed using thenon-sulfonated form of coumarin-NHS (AMCA-NHS) when used in standard E.coil S30 translation mixtures generated very low levels of detectablefluorescent bands when detected using UV light from a standard UVtransilluminator. In contrast, the sulfonated form (AMCA-sulfo-NHS) whenadded using the same procedures led to easily detectable bands using theUV-transilluminator.

Attempts to incorporate coumarin using an initiator tRNA by modifyingthe α-amino group of methionine have been reported in the literature butfailed. Coumarin attachment to a initiator tRNA subsequently requiredmore extensive and complicated chemical attachment using a chemicalcross linker. This was achieved by first aminoacylating the tRNA withmethionine followed by reaction of aminoacylated tRNA with DTDGmonosuccinimidyl ester (DTDG is Dithiodiglycolic acid). The reactionproduct was then reduced using DTT and subsequently reacted with CPM(3-(4′-Maleimidophenyl)-4-methyl-diethylamino coumarin. (Odom, O. W,Kudlicki, W and Hardesty, B. 1998. In vitro engineering usingacyl-derivatized tRNA, In Protein synthesis: Methods and Protocols, PP.93-103, Humana press, Totowa, N.J.). Due to the need for specialprocedures designed for each marker, such an approach is not practicalfor general attachment of a wide variety of markers to tRNAs throughpost-chemical aminoacylation procedures.

One likely factor that makes sulfonated NHS reagents used forpostchemical aminoacylation of tRNAs is its solubility in aqueousbuffer. In contrast, non-sulfonated reagents such as the BIDOPY FL NHSreagent require organic buffer such as DMSO for postchemicalmodification. While it is still not clear why use of organic bufferslowers the overall marker incorporation, one possibility is thathydrolysis of the aminoacyl bond formed between the amino acid and tRNAreduces the overall level of modification.

EXAMPLE 15 Imparting Water Solubility

In general, the property of water solubility can be imparted to chemicalreagents in several ways. Some of these are summarized below:

-   -   Introduction of polar functional group into leaving group (such        as sulfonated-NHS).    -   Introduction of the polar functional group into a spacer arm.    -   Introduction of the polar functional group into the reagent        moiety itself.

While the introduction of the —SO₃ ⁻Na⁺ (sulfo-) group is preferred,other polar ionizable groups (such as DSP) can also be used where DSP isshown below:

Final water soubility can be engineered into a spacer arm for example byusing a polyether spacer (e.g. one based on tetraethylene glycol). Ingeneral, any moiety that has a free carboxyl group can be converted intoits sulfa-NHS active ester. This reaction involvesN-hydroxy-sulfosuccinimide (monosodium salt), the marker and a couplingagent such as DCC (dicyclohexylcarbodiimide):

In a typical reaction, marker 1, 55 mmol, is dissolved in 10 ml DMF(dimethylformamide) and (2) (5 mmol) is added, followed by (3) (1.1equivalents). The mixture is stirred overnight at room temperature,precipitate filtered off, and the filtrate evaporated under reducedpressure at room temperature. The product is purified if necessary usingcolumn chromatography or is recrystallized.

One preferred embodiment of this invention involves the post-chemicalmodification of tRNAs to form a misaminoacylated tRNA by using markersthat contain a sulfonated NHS reagent. While such reagents are notgenerally available commercially, such reagents can be routinelyproduced out of a variety of useful markers. For example, fluoroescein,which has a high fluorescent quantum yield for both UV and visibleexcitation could be prepared in a form which contains a sulfonated NHSester.

EXAMPLE 16 Triple Marker System

In this example, a three marker system is employed to detect nascentproteins, i.e. an N-terminus marker, a C-terminus marker, and anaffinity marker (the latter being an endogenous affinity marker). Theexperiment involves 1) preparation of a tRNA with a marker, so that amarker can be introduced (during translation) at the N-terminus of theprotein; 2) translation of hemolysin with nucleic acid coding for wildtype and mutant hemolysin; and 4) quantitation of the markers.

1. Preparation of Biotin-Methionyl-tRNA^(fmet)

The purified tRNA^(fmet) (Sigma Chemicals, St. Louis, Mo.) was firstaminoacylated with methionine. The typical aminoacylation reactioncontained 1500 picomoles (−1.0 OD₂₆₀) of tRNA, 20 mM imidazole-HClbuffer, pH 7.5, 10 mM MgCl₂, 1 mM methionine, 2 mM ATP, 150 mM NaCl andexcess of aminoacyl tRNA-synthetases (Simla). The reaction mixture wasincubated for 45 min at 37° C. After incubation, the reaction mixturewas neutralized by adding 0.1 volume of 3 M sodium acetate, pH 5.0 andsubjected to chloroform:acid phenol extraction (1:1). Ethanol (2.5volumes) was added to the aqueous phase and the tRNA pellet obtained wasdissolved in the water (25 μl). The coupling of NHS-biotin to theα-amino group of methionine was carried out in 50 mM sodium bicarbonatebuffer, pH 8.0 by incubating the aminoacylated tRNA^(fmet) (25 μl) withNHS-biotin (final concentration=2 mM) for 10 min at 0° C. and thereaction was quenched by the addition of free lysine (finalconcentration=100 mM). The modified tRNA was precipitated with ethanoland passed through Sephadex G-25 gel filtration column (0.5×5 cm) toremove any free reagent, if present.

2. In vitro Translation of α-HL DNA

A WT and Amber (at position 135) mutant plasmid DNA was using coding forα-hemolysin (α-HL), a 32 kDa protein bearing amino acid sequenceHis-His-His-His-His-His (His-6) at its C-terminal. In vitro translationof WT and amber mutant α-HL gene (Amb 135) was carried out using E. coliT7 circular transcription/translation system (Promega Corp., Wisconsin,Wis.) in presence of Biotin-methionyl-tRNA^(fmet) (AmberGen, Inc.).Thetranslation reaction of 100 μl contained 30 μl E. coli extract (PromegaCorp., Wisconsin, Wis.), 40 μl premix without amino acids, 10 μl aminoacid mixture (1 mM), 5 μg of plasmid DNA coding for WT and mutant α-HL,150 picomoles of biotin-methionyl-tRNA^(fmet) and RNase-free water. Thepremix (1×) contains 57 mM HEPES, pH 8.2, 36 mM ammonium acetate, 210 mMpotassium glutamate, 1.7 mM DTT, 4% PEG 8000, 1.25 mM ATP, 0.8 mM GTP,0.8 mM UTP, 0.8 mM CTP, 60 mM phosphoenol pyruvate, 0.6 mM cAMP and 6 mMmagnesium acetate. From the translation reaction premix,n-formyl-tetrahydrofolate (fTHF) was omitted. The translation wascarried out at 37° C. for 1 hour. The translation reaction mixtureincubated without DNA is taken as control. After the translationreaction mixture was diluted with equal volume of TBS (Tris-bufferedsaline, pH 7.5). Each sample was divided into two aliquots and processedindividually as described below.

3. Preparation of Anti-α-HL Antibody Microtiter Plate

Anti-rabbit-IgG coated microtiter plate (Pierce Chemicals, Rockford,Ill.) was washed with Superblock buffer solution (Pierce) and incubatedwith 100 μg/ml of anti-α-HL polyclonal antibody solution (SigmaChemicals, St. Louis, Mo.) prepared in Superblock buffer on microtiterplate shaker for 1 hour at room temperature. The plate was then washed(3 times×200 μl) with Superblock buffer and stored at 4° C. till furtheruse.

4. Quantitation of N-terminal (Biotin) Marker

The translation reaction mixture (50 μl) for the control, WT and amberα-HL DNA were incubated in different wells of anti-α-HL microtiter platefor 30 minutes on the shaker at room temperature. After incubation, thewells were washed 5 times (5-10 min each) with 200 μl Superblock bufferand the supernatant were discarded. To these wells, 100 μl of 1:1000diluted streptavidin-horse radish peroxidase (Streptavidin-HRP; 0.25mg/ml; Promega) was added and the plate was incubated at roomtemperature for 20 min under shaking conditions. After the incubation,excess streptavidin-HRP was removed by extensive washing with Superblockbuffer (5 times×5 min each). Finally, 200 μl of substrate for HRP (OPDin HRP buffer; Pierce) was added and the HRP activity was determinedusing spectrophotometer by measuring absorbance at 441 nm.

5. Quantitation of C-terminal (His-6-taq) Marker

Translation reaction mixture (50 μl) from example 2 for control, WT andAmber α-HL DNA were incubated in different wells of anti-α-HL microtiterplate for 30 min on the shaker at room temperature. After incubation,the wells were washed 5 times (5-10 min each) with 200 μl Superblockbuffer and the supernatant were discarded. To these wells, 100 μl of1:1000 diluted anti-His-6 antibody (ClonTech, Palo Alto, Calif.) wasadded to the well and incubated at room temperature for 20 min undershaking conditions. After the incubation, excess antibodies were removedwith extensive washing with Superblock buffer (5 times×5 min each).Subsequently, the wells were incubated with secondary antibody(anti-mouse IgG-HRP, Roche-BM, Indianapolis, Ind.) for 20 min at roomtemperature. After washing excess 2^(nd) antibodies, HRP activity wasdetermined as described above.

6. Gel-Free Quantitation of N- and C-Terminal Markers

The results of the above-described quantitation are shown in FIG. 23A(quantitation of N-terminal, Biotin marker) and FIG. 23B (quantitationof C-terminal, His-6 marker). In case of in vitrotranscription/translation of WT α-HL DNA in presence ofbiotin-methionyl-tRNA, the protein synthesized will have translatedHis-6 tag at the C-terminal of the protein and some of the α-HLmolecules will also carry biotin at their N-terminus which has beenincorporated using biotinylated-methionine-tRNA. When the totaltranslation reaction mixture containing α-HL was incubated on toanti-α-HL antibody plate, selectively all the α-HL will bind to theplate via interaction of the antibody with the endogenous affinitymarker. The unbound proteins can be washed away and the N- andC-terminal of the bound protein can be quantitated usingStreptavidin-HRP and anti-His-6 antibodies, respectively. In case of WTα-HL, the protein will carry both the N-terminal (biotin) and C-terminal(His-6) tags and hence it will produce HRP signal in both the caseswhere streptavidin-HRP and secondary antibody-HRP conjugates againstHis-6 antibody used (HL, FIG. 23A). On the other hand, in case of ambermutant α-HL, only N-terminal fragment of α-HL (first 134 amino acids)will be produced and will have only N-terminal marker, biotin, but willnot have His-6 marker due to amber mutation at codon number 135. As aresult of this mutation, the protein produced using amber α-HL DNA willbind to the antibody plate but will only produce a signal in the case ofstrepavidin-HRP (HL-AMB, FIG. 23A) and not for anti-His×6 antibodies(HL-AMB, FIG. 23B).

EXAMPLE 17 Electrophoretic Mobility Shift Assay

To demonstrate the changes in the electrophoretic mobility offluorescently labeled nascent protein on the SDS-gels either due toproteolysis or oligomerization in presence of membranes, we have useplasmid DNA of α-hemolysin (α-HL) which codes 32 kDa protein bearing asequence His-His-His-His-His-His (His-6) at its C-terminal. In vitrotranslation of α-HL gene was carried out using E. coli T7 circulartranscription/translation system (Promega Corp., Wisconsin-Madison,Wis.) in presence of BODIPY-FL-methionyl-tRNA^(fmet) (AmberGen, Inc.)This experiment involved 1) preparation of the tRNA-marker forintroduction of the N-terminus marker during translation, 2)translation, 3) purification, 4) protease treatment or 5)oligomerization.

1. Preparation of BODIPY-FL-methionyl-tRNA:

BODIPYL-FL-methionyl-tRNA was prepared by first aminoacylating puretRNA^(fmet) (Sigma Chemicals, St. Louis, Mo.) using methionine andsubsequently modifying α-amino group of methionine using BODIPY-FL-SSE(4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene propionic acid,sulfosuccinimidyl ester; Molecular Probes, Eugene, Oreg.). The typicalaminoacylation reaction (100 μl) to contained 1500 picomoles (−1.0OD₂₆₀) of tRNA, 20 mM imidazole-HCI buffer, pH 7.5, 10 mM MgCl₂, 1 mMmethionine, 2 mM ATP, 150 mM NaCI and excess of aminoacyltRNA-synthetases (Sigma). The reaction mixture was incubated for 45 minat 37° C. After incubation, the reaction mixture was neutralized byadding 0.1 volume of 3 M sodium acetate, pH 5.0 and subjected tochloroform:acid phenol extraction (1:1). Ethanol (2.5 volumes) was addedto the aqueous phase and the tRNA pellet obtained was dissolved in thewater (25 μl). The coupling of BODIPY-FL-SSE to the α-amino group ofmethionine was carried out in 50 μl reaction volume using 50 mM sodiumbicarbonate buffer, pH 8.0 by incubating 25 μl aminoacylated tRNA^(fmet)(1.5 nanomoles) with 10 μl of BODIPY-FL-SSE (10 mM) for 10 min at 0° C.and the reaction was quenched by the addition of free lysine (finalconcentration=100 mM). The modified tRNA was precipitated with ethanol,and the pellet was dissolved in RNase-free water and passed throughSephadex G-25 gel filtration column (0.5×5 cm) to remove any freefluorescent reagent, if present.

2. In vitro Translation of α-hemolysin DNA

The translation reaction of 100 μL contained 30 μl E. coli extract(Promega Corp., Wisconsin, Wis.), 40 μl premix without amino acids, 10μl amino acid mixture (1 mM), 5 μg of plasmid DNA coding for α-HL, 150picomoles of BODIPY-FL-methionyl-tRNA^(fmet) and RNase free water. Thepremix (1×) contains 57 mM HEPES, pH 8.2, 36 mM ammonium acetate, 210 mMpotassium glutamate, 1.7 mM DTT, 4% PEG 8000. 1.25 mM ATP, 0.8 mM GTP,0.8 mM UTP, 60 mM phosphoenol pyruvate, 0.6 mM cAMP and 6 mM magnesiumacetate. From the translation reaction premix, n-formyl-tetrahydrofolate(fTHF) was omitted. The translation was carried out at 37° C. for 1hour. The translation reaction mixture incubated without DNA is taken ascontrol.

3. Purification of Hls-6-α-HL

Fifty microliters of the translation reaction mixture (from above) wassubjected to Talon-Sepharose (ClonTech, Palo Alto, Calif.)chromatography for the purification of Hls-6-α-HL. This was carried outby loading the crude extract onto the Talon-Sepharose column which waspre-equilibrated with 50 mM Tris-HCl, pH 8.0 containing 150 mM NaCI andwashing the column to remove unbound proteins. The bound protein wasthen eluted by adding 100 mM imidazole in the above buffer. The elutedα-HL was dialyzed against 50 mM Tris-HCl buffer, pH 7.5.

4. EMSA for Protease Detection

The purified fluorescently labeled α-HL (−5 μg) (example 3) wasincubated with 0.0.5 μg of pure trypsin (Sigma Chemicals, St. Louis,Mo.) in 50 nM acetate buffer, pH 5.0 (100:1; protein:protease ratio) for5 min at 37° C. The proteolysis reaction was arrested by the addition of1× SDS-gel loading buffer and boiling the samples for 5 min. TheSDS-PAGE was carried out as described by Laemmli (Laemmli, U. K. 1970,Nature 227, 680-685) using 4-20% gradient gel (ready-gel, Bio-Rad,Richmond, Calif.). After the gel electrophoresis, the gel was visualizedusing FluorImager F595 (Molecular Dynamics, Sunnyvale, Calif.).

Trypsin was used under very limited conditions (single-hit kinetics) toobtain very defined cleavage of α-HL (50 mM acetate buffer, pH 5.0,100:1: protein:protease ratio, 5 min at 37° C.). Under these conditions,the glycine rich loop in α-HL is most susceptible to cleavage and as aresult proteolytic fragment of 17 kDa was observed (Vecesey-Semjen, B.,Knapp, S., Mollby, R., Goat, F. G. 1999, Biochemistry, 38 4296-4302).When the fluorescently labeled α-HL was subjected to very mild trypsintreatment, it resulted a cleavage of α-HL yielding the N-terminalfragment of approximately 17-18 kDa mass as evidence by change in themobility of fluorescent band on SDS-PAGE (FIG. 24: Lane 1 showsuntreated protein and Lane 2 shows protease treated protein). Thisresult indicates that such assay could be used to screen for proteasesor any other enzymatic activities like kinase, transferase etc. thatcould potentially result in the electrophoretic mobility shift of thenascent protein. Though we have used pure nascent protein for thisparticular assay, there is no reason why one can not use a nascentprotein without any purification (total translation reaction mixture).

5. EMSA for Oligomerization of Nascent Protein on Membranes

The total translation reaction mixture (10 μl) (see above) was incubatedin absence and in presence of rabbit red blood cells (rRBCs, CharlesRiver Farm, Conn.) for 30 min. at 0° C. After the incubation, rRBCs werewashed free of excess unbound α-HL and the rRBCs were incubated in Trisbuffer saline (TBS) containing 1 mg/ml BSA (TBSA) at 37° C. for 20 minduring which lysis of rRBCs occurred. The rRBC membranes were isolatedafter centrifugation, dissolved in 1× SDS-gel loading buffer andsubjected to SDS-PAGE (4-20% gradient gel) without heating the sample.After the gel electrophoresis, the gel was visualized using FluorImagerF595.

α-HL is expressed a soluble monomeric protein and in presence of variousmembranes it can oligomerize to form heptameric pore (Walker, B.,Krishnasastry, M., Zorn, L., Kasianowicz, J. and Bayley, H., 1992, J.Biol. Chem. 267, 10902-10909). In addition, some intermediate forms ofthe oligomers were also observed. In this experiment, in order to seethe applicability of EMSA to detect the shift in mobility of α-HL due tooligomerization in presence lipid membranes, the total translationreaction mixture (with out any purification) was used. When the totaltranslation extract containing nascent α-HL was incubated with rRBCs, itresulted in the oligomerization of α-HL on the rRBC membranes yielding adistinct fluorescent bands corresponding to various molecular massesthat were SDS-resistant (FIG. 25: Lane 1 shows untreated protein onlyand Lane 2 shows protein treated with rRBCs).

This result demonstrates that such assay could be used to studyproteins, interact with variety of natural and artificial membranes andas a result the mobility of the protein in shifted.

EXAMPLE 18 Incorporation Using Lysyl-tRNA^(lys)

This example describes the incorporation of fluorescent labels intonascent protein using lysyl-tRNA^(lys). More specifically, a variety offluorescent molecules were incorporated into 1) hemolysin duringtranslation in an E coli translation system, and 2) luciferase duringtranslation in a wheat germ system, using lysyl tRNA^(lys). Theexperiment involved 1) preparation of the tRNA-marker compounds, 2)translation, and 3) detection on gels.

1. Preparation of Fluorescent Labeled Misaminoacylated tRNA^(lys)

The purified tRNA^(lys) (Sigma Chemicals, St. Louis, Mo.) was firstamino-acylated with lysine. The typical aminoacylation reaction (100 μl)contained 1500 picomoles (−1.0 OD₂₆₀) of tRNA, 20 mM imidazole-HClbuffer, pH 7.5, 10 mM MgCl₂, 1 mM lysine, 2 mM ATP, 150 mM NaCl andexcess of aminoacyl tRNA-synthetases (Sigma). The reaction mixture wasincubated for 45 min at 37° C. After incubation, the reaction mixturewas neutralized by adding 0.1 volume of 3 M sodium acetate, pH 5.0 andsubjected to chloroform:acid phenol extraction (1:1). Ethanol (2.5volumes) was added to the aqueous phase and the tRNA pellet obtained wasdissolved in the water (25 μl). The coupling of NHS-derivatives ofvarious fluorescent molecules (see Table 2) to the ε-amino group oflysine was carried out in 50 mM CAPS buffer, pH 10.5 by incubating theaminoacylated tRNA^(lys) (25 μl) with fluorescent reagent (finalconcentration=2 mM) for 10 min at 0° C. and the reaction was quenched bythe addition of free lysine (final concentration=100 mM). The modifiedtRNA was precipitated with ethanol, dissolved in 50 μl of RNase-freewater and passed through Sephadex G-25 gel filtration column (0.5×5 cm)to remove any free fluorescent reagent, if present. The modified tRNAwas stored frozen (−70° C.) in small aliquots in order to avoidfree-thaws. The modification extent of the aminoacylated-tRNA wasassessed by acid-urea gel electrophoresis (Varshney, U., Lee, C. P. &RajBhandary, U. L., 1991 J. Biol. Chem. 266, 24712-24718).

2. Cell Free Synthesis of Proteins in Prokaryotic (E. coli) TranslationExtracts

The typical translation reaction mixture (10 μl) contained 3 μl of E.coli extract (Promega Corp., Wisconsin-Madison, Wis.), 4 μl of premix, 1μl of amino acid mix (1 mM), 30 picomoles of fluorescent-lysyl-tRNA and0.5 μg of α hemolysin (αHL) plasmid DNA. The premix (1×) contains 57 mMHEPES, pH 8.2, 36 mM ammonium acetate, 210 mM potassium glutamate, 1.7mM DTT, 4% PEG 8000, 1.25 mM ATP, 0.8 mM GTP, 0.8 mM CTP, 60 mMphosphoenal pyruvate, 0.6 mM cAMP and 6 mM magnesium acetate. Thetranslation reaction was allowed to proceed for 45 min at 37° C. ForSDS-PAGE, 4-10 82 l aliquot of the reaction mix was precipitated with5-volume acetone and the precipitated proteins were collected bycentrifugation. The pellet was dissolved in 1× loading buffer andsubjected to SDS-PAGE after boiling for 5 min. SDS-PAGE was carried outaccording to Laemmmli (Lammli, U.K. 1970, Nature, 227, 680-685).

3. Cell-Free Synthesis in Eukaryotic (TnT Wheat Germ) TranslationExtracts.

The typical translation reaction mixture (10 μl) contained 5 μl of TnTwheat germ extract (Promega Corp., Wisconsin-Madison, Wis.), 0.4 μl ofTnT reaction buffer, 1 μof amino acid mix (1 mM), 0.2 μl of T7 RNApolymerase, 30 picomoles of fluorescent-lysyl-tRNA and 0.5 μg ofluciferase RNA (Promega) and RNase-free water. The translation reactionwas allowed to proceed for 45 min at 30° C. and reaction mixture wascentrifuged for 5 min to remove insoluble material. The clarifiedextract was then precipitated with 5-volume acetone and the precipitatedproteins were collected by centrifugation. The pellet was dissolved in1× loading buffer and subjected to SDS-PAGE after boiling for 5 min.SDS-PAGE was carried out according to Laemmli (Lammli, U.K. 1970),Nature, 227, 680-685).

4. Detection of Nascent Protein

The gel containing nascent proteins was scanned using FluorImager F595(Molecular Dynamics, Sunnyvale, Calif. using Argon laser (488 nm) asexcitation source, in addition, the nascent proteins in polyacrylamidegels were also detected using an UV-transilluminator and the photographswere carried out using Polaroid camera fitted with Tiffen green filter(Polaroid, Cambridge, Mass.). FIGS. 26A and 26B show the results of invitro translation of α-HL produced in presence of various fluorescenttRNA^(lys). It is clear from the results one can incorporate a varietyof fluorescent molecules into nascent protein using misaminoacylatedtRNA (fluorophore-modified lysyl-tRNA^(lys)) including dyes like NBD,fluorescein derivatives etc. (Lane 1: No DNA control; lane 2:BODIPY-FL-SSE (4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacenepropionic acid, sulfosuccinimidyl ester); lane 3: BODIPY-FL-SE(4,4-difluoro-5,7-dimethyl-4bora-3a, 4a-diaza-s-indacene proionic acid,succinimidyl ester); lane 4: NBD-X-SE (Succinimidyl6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminohexanoate); lane 5;BODIPY-TMR-SE((6-994,4-difluoro-1,3-dimethyl-5-(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene-2-propionyl)amino)hexanoic acid, succinimidylester); lane 6: BODIPY-R6G-SE((4,4-difluoro-5-phenyl-4-bora-3a,4a-diaza-s-indacene-3propionic acid,succinimidyl ester); lane 7; FAM-SE (5-(6-)-carboxyfluorescein,succinimidyl ester); lane 8:SFX-SE (6-fluorescein-5-(and6-)carboxyamido)hexonoic acid, succinimidyl ester); lane 9:PyMPO-SE(1-(3-(succinimidyloxycarbonyl)benzyl)-4-(5-(4-methoxyphenyl)oxazol-2-yl)pyridininiumbromide (PyMPO)) and lane 10: TAMRA-SE(6-(tetramethylrhodamine-5-(and-6)-carboxamido)hexanoic acid,succinimidyl ester).

EXAMPLE 19 NHS-Derivatives of Coumarin

Given the above noted results for the two BODIPY molecules (i.e.BODIPY-FL-SSE and BODIPY-FL-SE), attempts were made to derivatize othermarkers to make them suitable for incorporation. The present exampleinvolves 1) the preparation of the labeled tRNA, 2) translation, and 3)detection of the nascent protein containing the label (or marker).

1. Preparation of Fluorescent Labeled Misaminoacylated tRNA^(fmet)

The purified tRNA^(fmet) (Sigma Chemicals, St. Louis, Mo.) was firstaminoacylated with methionine. The typical aminoacylation reaction (100μl) contained 1500 picomoles (approximately 1.0 OD₂₅₀) of tRNA, 20 mMimidazole-HCI buffer, pH 7.5, 10 mM MgCl₂, 1 mM lysine, 2 mM ATP, 150 mMNaCl and excess of aminoacyl tRNA-synthetases (Sigma). The reactionmixture was incubated for 45 min at 37° C. After incubation, thereaction mixture was neutralized by adding 0.1 volume of 3 M sodiumacetate, pH 5.0 and subjected to chloroform:acid phenol extraction(1:1). Ethanol (2.5 volumes) was added to the aqueous phase and the tRNApellet obtained was dissolved in the water (25 μl). The coupling ofNHS-derivatives of coumarin [namely sulfosuccinimidyl7-amino-4-methylcoumarin-3-acetate [1] (AMCA-sulfo-NHS; PierceChemicals), Alexa 350-N-hydroxy-succinimide ester (Molecular Probes) andsuccinimidyl 7-amethyl-amino-coumarin acetate (AMCA-NHS: MolecularProbes)] to the α-amino group of methionine was carried out in 50 mMsodium bicarbonate buffer, pH 8.5 by incubating the aminoacylatedtRNA^(fmet) (25 μl) with fluorescent reagent (final concentration=2 mM)for 10 min at 0° C. and the reaction was quenched by the addition offree lysine (final concentration=100mM). In case of AMCA-NHS, reagentwas dissolved in DMSO and the coupling reaction was carried out inpresence of 40% DMSO. The modified tRNA was precipitated with ethanol,dissolved in 50 μl of RNase-free water and passed through Sephadex G-25gel filtration column (0.5×5 cm) to remove any free fluorescent reagent,if present. The modified tRNA was stored frozen (−70° C.) in smallaliquots in order to avoid free-thaws. The modification extent of theaminoacylated-tRNA was assessed by acid-urea gel electrophoresis(Varshney, U., Lee, C. P. & RajBhandary, U. L., 1991, J. Biol. Chem.266, 24712-24718).

2. Cell Free Systhesis of Proteins in Prokaryotic (E. coli) TranslationExtracts:

The typical translation reaction mixture (10 μl) contained 3 μl of E.coli S-30 extract (Promega Corp., Wisconsin-Madison, Wis.), 4 μl ofpremix, 1 μ1 of amino acid mix (1 mM), 30 picomoles offluorescent-methionyl-tRNA and 0.5 μg of α-hemolysin (α-HL) plasmid DNA.The premix (1×) contains 57 mM HEPES, pH 8.2, 36 mM ammonium acetate,210 mM potassium glutamate, 1.7 mM DTT, 4% PEG 8000, 1.25 mM ATP, 0.8 mMGTP, 0.8 mM UTP, 0.8 mM CTP, 60 mM phosphoenol pyruvate, 0.6 mM cAMP and6 mM magnesium acetate. The translation reaction was allowed to proceedfor 45 min at 37° C. For SDS-PAGE, 4-10 μl aliquot of the reaction mixwas precipitated with 5-volume acetone and the precipitated proteinswere collected by centrifugation. The pellet was dissolved in 1× loadingbuffer and subjected to SDS-PAGE after boiling for 5 min. SDS-PAGE wascarried out according to Laemmli (Laemmli, U. K. 1970, Nature, 277,680-685).

3. Detection of Nascent Protein

The gel containing nascent proteins was visualized using anUV-transilluminator equipped with long wavelength UV bulb (>300 nm) andthe photographs were carried out using Polaroid camera fitted withTiffen green filter (Polaroid, Cambridge, Mass.). FIG. 27 indicates thatthe result in vitro translation of α-HL produced in presence of variousfluorescent tRNAs (Lane 1 shows the results for the no DNA control; Lane2 shows the results with Met-tRNA^(fmet) modified with AMCA-NHS; Lane 3shows the results with Met-tRNA^(fmet) modified with AMCA-sulfo-NHS; andLane 4 shows the results with Met-tRNA^(fmet) modified with Alexa-NHS).Clearly, one can incorporate the coumarin derivative molecules intonascent protein using misaminoacylated tRNA which are modified with thewater soluble NHS-esters of fluorescent molecules (lane 3). Moreover, adye with negative charge (Alexa, lane 4) seems to not incorporate aswell as its neutral counterpart (AMCA; lane 3).

From the above results and general teachings of the presentspecification, one skilled in the art can select other markers andrender them (e.g. chemically render them) suitable for incorporation inaccordance with the methods of the present invention.

EXAMPLE 20 Capillary Electrophoresis

The example describes the use of capillary electrophoresis (CE) fordetection of in vitro synthesized fluorescent proteins by mobilityshift. The example describes 1) the preparation of the tRNA comprising aBODIPY marker, 2) in vitro translation, 3) purification, 4) proteasedigestion and 5) detection by mobility shift assay.

1. Preparation of BODIPY-FL-methionyl-tRNA^(fmet)

The tRNA^(fmet) was aminoacylated with the methionine. In typicalreaction, 1500 picomoles (˜1.0 OD₂₆₀) of tRNA was incubated for 45 minat 37° C. in aminoacylation mix using an excess of aminoacyltRNA-synthetases. The aminoacylation mix comprised 20 mM imidazole-HClbuffer, pH 7.5, 150 mM NaCl, 10 mM MgCl₂, 2 mM ATP and 1600 units ofaminoacyl tRNA-synthetase. The extent of aminoacylation was determinedby acid-urea gel as well as by using ³⁵S-methionine. After incubation,the mixture was neutralized by adding 0.1 volume of 3 M sodium acetate,pH 5.0 and subjected to chloroform:acid phenol (pH 5.0) extraction(1:1). Ethanol (2.5 volumes) was added to the aqueous phase and the tRNApellet obtained was dissolved in water (37.5 ul) and used formodification. To the above aminoacylated-tRNA solution, 2.5 ul of INNaHCO₃ was added (final conc. 50 mM, pH=8.5) followed by 10 ul of 10 mMsolution of BODIPY-FL-SSE (Molecular Probes) in water. The mixture wasincubated for 10 min at 0° C. and the reaction was quenched by theaddition of lysine (final concentration=100 mM). To the resultingsolution 0.1 volume of 3 M NaOAc, pH=5.0 was added and the modified tRNAwas precipitated with 3 volumes of ethanol. Precipitate was dissolved in50 ul of water and purified on Sephadex G-25 gel filtration column(0.5×5 cm) to remove any free fluorescent reagent, if present. Themodified tRNA was stored frozen (−70° C.) in small aliquots in order toavoid free-thaws.

2. In vitro Translation of α-Hemolysin DNA

The translation reaction of 500 ul contained 150 ul E. coli extract(Promega Corp., Wisconsin, Wis.), 200 ul premix without amino acids, 50ul amino acid mixture (1 mM), 25 ug of plasmid DNA coding for α-HL, 1000picomoles of BODIPY-FL-methionyl-tRNA^(fmet) and RNase free water. Thepremix (1×) contains 57 mM HEPES, pH 8.2, 36 mM ammonium acetate, 210 mMpotassium glutamate, 1.7 mM DTT, 4% PEG 8000, 1.25 mM ATP, 0.8 mM GTP,0.8 mM UTP, 0.8 mM CTP, 60 mM phosphoenol pyruvate, 0.6 mM cAMP and 16mM magnesium acetate. From the translation reaction premix,n-formyl-tetrahydrofolate (fTHF) was omitted. The translation wascarried out at 37° C. for 1 hour. The translation reaction mixtureincubated without DNA is taken as control.

3. Purification of His-6-α-HL

Five hundred microliters of the translation reaction mixture (see step 2above) was subjected to Talon-Sepharose (ClonTech, Polo Alto, Calif.)chromatography for the purification of His-6-α-HL. This was carried outby loading the crude extract onto the

Talon-Sepharose column which was pre-equilibrated with 50 mM Tris-HCl,pH 8.0 containing 150 mM NaCl and washing the column to remove unboundproteins. The bound protein was then eluted by adding 100 mM imidazolein the above buffer. The eluted α-HL was dialyzed against 50 mM Tris-HClbuffer, pH 7.5. The fluorescence of purified and dialyzed α-HL waschecked on Molecular Dynamics FluorImager F595.

4. Protease Digestion

The purified fluorescently labeled α-HL (˜5 ug) (see step 3 above) wasincubated with 0.1 ug of pure trypsin (Sigma Chemicals, St. Louis, Mo.)in 50 mM Tris-HCl buffer, pH 7.5 (50:1; protein:protease ratio) for 10min at room temperature. The proteolysis reaction was arrested by theaddition of 1× CE-SDS-gel loading buffer and boiling the samples for 10min.

5. Mobility Shift Assay

The SDS-capillary gel electrophoresis (SDS-CGE) was performed on aBio-Rad BioFocus 3000CE system. The capillary was fused-silica with a 75uM ID, 24 cm total length and 19.5 cm to the detector. Fifty microlitersof fluorescently labeled protein sample (α-HL) was mixed with 50 ul ofSDS-CGE sample loading buffer and incubated at 95° C. for 10 min. Thecapillary was rinsed with 0.1 M NaOH, 0.1 M HCl and SDS-run buffer for60, 60 and 120 sec respectively, prior to each injection. Sample wereinjected using electrophoretic injection (20 sec at 10 kV). Separationwas performed at 15 kV (constant voltage) for 25 min. Capillary andsample was maintained at 20° C. The detection of sample was carried outusing 488 nm Argon laser and 520 nm emission filter.

The results of SDS-CGE are shown in the FIG. 28. As seen in the Figure,fluorescently label α-HL migrates as a major species eluting around 24min under the electrophoresis conditions (Top panel). In addition, theelectrophoregram also show the presence of minor impurities present inthe sample, which are eluting around 17 and 20.5 min. When thefluorescently labeled-α-HL sample was treated with trypsin and analyzedusing SDS-CGE, it showed peaks eluting earlier (13, 14 and 15 min) andmajor peak at 21 min (Bottom panel). This result indicated that the α-HLwas proteolysed by the trypsin and various proteolytic fragments haveN-terminal fluorescently labeled are seen in the electrophoregram.

EXAMPLE 21 Incorporation of Three Markers

This is an example wherein a protein is generated in vitro underconditions where N- and C-terminal markers are incorporated along with amarker incorporated using a misaminoacylated tRNA. The Exampleinvolves 1) PCR with primers harboring N-terminal and C-terminaldetectable markers, 2) preparation of the tRNA, 3) in vitro translation,4) detection of nascent protein.

1, PCR of α-Hemolysin DNA

Plasmid DNA for α-hemolysin, pT7-WT-H6-αHL, was amplified by PCR usingfollowing primers. The forward primer (HL-5) was:5’-GAATTC-TAATACGACTCACTATAGGGTTAACTTTAAGAAGGAGATATACATATGGAAC AAAAATTAATCTCGGAAGAGGATTTGGCAGATTCTGATATTAATATTAAAA CC-3′ and the reverseprimer (HL-3) was: 5′-AGCTTCATTAATGATGGTGATGG-TGGTGAC 3′. The underlinedsequence in forward primer is T7 promoter, the region in boldcorresponds to ribosome binding site (Shine-Dalgarno's sequence), thebold and underlined sequences involve the C-myc epitope and nucleotidesshown in italics are the complimentary region of α-hemolysin sequence.In the reverse primer, the underlined sequence corresponds to that ofHis×6 epitope. The PCR reaction mixture of 100 ul contained 100 ngtemplate DNA, 0.5 uM each primer, 1.mM MgCl₂, 50 ul of PCR master mix(Qiagen, CA) and nuclease free water (Sigma Chemicals, St. Louis, Mo.)water. The PCR was carried out using Hybaid Omni-E thermocyler (Hybaid,Franklin, Mass.) fitted with hot-lid using following conditions: 95° C.for 2 min, followed by 35 cycles consisted of 95° C. for 1 min, 61° C.for 1 min and 72° C. for 2 min and the final extension at 72° C. for 7min. The PCR product was then purified using Qiagen PCR clean-up kit(Qiagen, CA). The purified PCR DNA was used in the translation reaction.

2. Preparation of BODIPY-FL-lysyl-tRNA^(lys)

The purified tRNA^(lys) (Sigma Chemicals, St. Louis, Mo.) was firstaminoacylated with lysine. The typical aminoacylation reaction contained1500 picomoles (˜1.0 OD₂₆₀) of tRNA, 20 mM imidazole-HCl buffer, pH 7.5,10 mM MgCl₂, 1 mM lysine, 2 mM ATP, 150 mM NaCl and excess of aminoacyltRNA-synthetases (Sigma Chemicals, St. Louis, Mo.). The reaction mixturewas incubated for 45 min at 37° C. After incubation, the reactionmixture was neutralized by adding 0.1 volume of 3 M sodium acetate, pH5.0 and subjected to chloroform:acid phenol extraction (1:1). Ethanol(2.5 volumes) was added to the aqueous phase and the tRNA pelletobtained was dissolved in water (35 ul). To this solution 5 ul of 0.5 MCAPS buffer, pH 10.5 was added (50 mM final conc.) followed by 10 ul of10 mM solution of BODIPY-FL-SSE. The mixture was incubated for 10 min at0° C. and the reaction was quenched by the addition of lysine (finalconcentration=100 mM). To the resulting solution 0.1 volume of 3 MNaOAc, pH=5.0 was added and the modified tRNA was precipitated with 3volumes of ethanol. Precipitate was dissolved in 50 ul of water andpurified on Sephadex G-25 gel filtration column (0.5×5 cm) to remove anyfree fluorescent reagent, if present. The modified tRNA was storedfrozen (−70° C.) in small aliquots in order to avoid free-thaws. Themodification extent of the aminoacylated-tRNA was assessed by acid-ureagel electrophoresis. Varshney et al., J. Biol. Chem. 266:24712-24718(1991).

3. Cell-Free Synthesis of Proteins in Eukaryotic (Wheat Germ)Translation Extracts.

The typical translation reaction mixture (20 ul) contained 10 ul of TnTwheat germ extract (Promega Corp., Wisconsin-Madison, Wis.), 0.8 ul ofTnT reaction buffer, 2 ul of amino acid mix (1 mM), 0.4 ul of T7 RNApolymerase, 30 picomoles of BODIPY-FL-lysyl-tRNA^(lys), 1-2 ug plasmidor PCR DNA (Example 1) and RNase-free water. The translation reactionwas allowed to proceed for 60 min at 30° C. and reaction mixture wascentrifuged for 5 min to remove insoluble material. The clarifiedextract was then precipitated with 5-volumes of acetone and theprecipitated proteins were collected by centrifugation. The pellet wasdissolved in 1× loading buffer and subjected to SDS-PAGE after boilingfor 5 min. SDS-PAGE was carried out according to Laemmli, Nature,227:680-685.

4. Detection of Nascent Protein

After the electrophoresis, gel was scanned using FluorImager 595(Molecular Dymanics, Sunnyvale, Calif.) equipped with argon laser asexcitation source. For visualization of BODIPY-FL labeled nascentprotein, we have used 488 nm as the excitation source as it is theclosest to its excitation maximum and for emission, we have used530+/−30 filter. The gel was scanned using PMT voltage 1000 volts andeither 100 or 200 micron pixel size.

The results are shown in FIG. 29. It can be seen from the Figure thatone can in vitro produce the protein from the PCR DNA containing desiredmarker(s) present. In the present case, the protein (α-hemolysin) has aC-myc epitope at N-terminal and His×6 epitope at C-terminal. Inaddition, BODIPY-FL, a fluorescent reporter molecule is incorporatedinto the protein. Lane 1: α-Hemolysin plasmid DNA control; lane 2: noDNA control; lane 3: PCR α-hemolysin DNA and lane 4: hemolysin amber 135DNA. The top (T) and bottom (B) bands in all the lane are from thenon-specific binding of fluorescent tRNA to some proteins in wheat germextract and free fluorescent-tRNA present in the translation reaction,respectively.

EXAMPLE 22 Primer Design

It is not intended that the present invention be limited to particularprimers. A variety of primers are contemplated for use in the presentinvention to ultimately incorporate markers in the the nascent protein(as explained above). The Example involves 1) PCR with primers harboringmarkers, 2) in vitro translation, and 3) detection of nascent protein.

For PCR the following primers were used: forward primer: 5′GGATCCTAATACGACTCACTATAGGGAGACCACCATGGAACAAAAATTAATATCGGAAGAGGATTTGAATGTTTCTCCATACAGGTCACGGGGA-3′ Reverse Primer: 5′-TTATTA

TTCTGTAGGAATGGTATCTCGTTTTTC-3′ The underlined sequence in the forwardprimer is T7 promoter, the bold and underlined sequences involve theC-myc epitope and nucleotides shown in italics are the complimentaryregion of α-hemolysin sequence. In the reverse primer, the underlinedsequence corresponds to that of His×6 epitope. A PCR reaction mixture of100 ul can be used containing 100 ng template DNA, 0.5 uM each primer, 1mM MgCl₂, 50 ul of PCR master mix (Qiagen, CA) and nuclease free water(Sigma Chemicals, St. Louis, Mo.) water. The PCR can be carried outusing Hybaid Omni-E thermocyler (Hybaid, Franklin, Mass.) fitted withhot-lid using following conditions: 95° C. for 2 min, followed by 35cycles consisted of 95° C. for 1 min, 61° C. for 1 min and 72° C. for 2min and the final extension at 72° C. for 7 min. The PCR product canthen be purified using Qiagen PCR clean-up kit (Qiagen, CA). Thepurified PCR DNA can then be used in a variety of translation reactions.Detection can be done as described above.

Other embodiments and uses of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered exemplary only, with the scope of particularembodiments of the invention indicated by the following claims.

1. A composition, comprising a nascent protein bound to a surface,wherein said nascent protein comprises an N-terminal epitope marker anda C-terminal epitope marker incorporated into said nascent proteinduring translation, said N-terminal epitope marker bound to a firstbinding agent and said C-terminal epitope marker bound to a secondbinding agent.
 2. The composition of claim 1, wherein said surface is awell of a microtiter plate.
 3. The composition of claim 1, wherein saidnascent protein is encoded by a gene associated with a disease.
 4. Thecomposition of claim 1, wherein said surface comprises a bead surface.5. The composition of claim 1, wherein said surface comprises amicrofluidic device.
 6. A composition, comprising a nascent proteinbound to a surface, wherein said nascent protein comprises an N-terminalepitope marker and a C-terminal epitope marker incorporated into saidnascent protein during translation, said N-terminal epitope marker boundto a first antibody and said C-terminal epitope marker bound to a secondantibody.
 7. The composition of claim 6, wherein said surface is a wellof a microtiter plate.
 8. The composition of claim 6, wherein saidnascent protein is encoded by a gene associated with a disease.
 9. Thecomposition of claim 6, wherein said surface comprises a bead surface.10. The composition of claim 6, wherein said surface comprises amicrofluidic device.
 11. A microfluidic device comprising fluid, saidfluid comprising a nascent protein, wherein said nascent proteincomprises an N-terminal epitope marker and a C-terminal epitope markerincorporated into said nascent protein during translation.
 12. Themicrofluidic device of claim 11, wherein said device comprises channels.13. The microfluidic device of claim 12, wherein said channels arebetween approximately 0.10 and 0.50 micrometers in depth.
 14. A method,comprising: a) providing a microfluidic device and reagents fortranslating a nascent protein, and b) translating a nascent protein insaid microfluidic device, wherein said nascent protein comprises anN-terminal epitope marker and a C-terminal epitope marker incorporatedinto said nascent protein during translation.
 15. The method of claim14, wherein said device comprises channels.
 16. The method of claim 15,wherein said channels are between approximately 0.10 and 0.50micrometers in depth.